Commit graph

29755 commits

Author SHA1 Message Date
Kishon Vijay Abraham I
8d488f3e16 usb: dwc3: Add chained TRB support for ep0
dwc3 can do only max packet aligned transfers. So in case request length
is not max packet aligned and is bigger than DWC3_EP0_BOUNCE_SIZE
two chained TRBs is required to handle the transfer.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
1f78f8feda usb: dwc3: ep0: preparation for implementing chained TRB
No functional change. Modified few things so that there are no
code duplication while implementing chained TRB.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
526a50f8ec dwc3: flush the buffers before using it
In the linux kernel, non cacheable buffers are used. However in uboot
since there are no APIs to allocate non cacheable memory, all
the buffers should be flushed before using it.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
6900aeda52 usb: dwc3: TI PHY: PHY driver for dwc3 in TI platforms
Added a single driver for both USB2 PHY programming and USB3 PHY
programming.

USB3 PHY is taken from drivers/phy/phy-ti-pipe3.c in linux kernel.
commit 56042e : phy: ti-pipe3: Fix suspend/resume and module reload.

USB2 PHY is taken from drivers/phy/phy-omap-usb2.c in linux kernel.
commit eb82a3 : phy: omap-usb2: Balance pm_runtime_enable() on probe
failure and remove.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
53de33fc00 usb: dwc3: dwc3-omap: add interrupt status API to check for interrupts
Added an API to check for interrupt status. This API is generally
called from board file to check for interrupt status.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
57207657a1 dwc3: dwc3-omap: add support for multiple dwc3-omap controllers
Added support for multiple dwc3 omap controllers. This gives uboot
the capability to control multiple dwc3 omap controllers.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
c241d7eee4 usb: dwc3: dwc3-omap: change probe and remove to uboot init and uboot exit code
Removed probe and remove that are specific to linux and replaced it with
uboot init and uboot exit. These functions will be invoked from boardfile.

This will change once we have dwc3-omap driver adapted to use the uboot
driver model.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
93c3763810 include: dwc3-omap-uboot: add a structure for populating dwc3-omap platform data
Added a structure to populate dwc3 omap platform data. The board file should
populate these platform data before invoking dwc3 omap driver.

This will be removed once dwc3-omap driver is adapted to use the driver model.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
3f52e1b985 usb: dwc3: dwc3-omap: make dwc3-omap build in uboot
*) Changed the included header files to that used in u-boot.
*) Removed extcon_* APIs
*) Removed regulator_* APIs
*) Fixed other misc warnings
*) Added dwc3-omap.h to include the definitions of UTMI modes.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
27d3b89d33 dwc3: core: added an API to invoke irq handlers
Since interrupt support is not present in u-boot, added an
API to handle the interrupts in dwc3 core. This API can be
polled to handle the interrupts.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
793d347f53 dwc3: core: add support for multiple dwc3 controllers
Added support for multiple dwc3 controllers. This gives uboot
the capability to control multiple dwc3 controllers.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:10 +02:00
Kishon Vijay Abraham I
8e1906a81f dwc3: core: change probe and remove to uboot init and uboot exit code
Removed probe and remove that are specific to linux and replaced it with
uboot init and uboot exit. These functions will be invoked from boardfile.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
da0d9e42a3 include: dwc3-uboot: add a structure for populating platform data
Added a structure to populate dwc3 core platform data. The board file should
populate these platform data before invoking dwc3 driver.
This will be removed once we have dwc3 driver adapted to use the driver model.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
71744d0d06 usb: dwc3: core: make dwc3 core build in uboot
*) Changed the include header files to that used in u-boot.
*) Removed phy_* APIs
*) Removed jiffies and used a simple while loop
*) Used dma_alloc_coherent and dma_free_coherent APIs of u-boot
*) Fixed other misc warnings

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
6f80390691 include: usb: composite: add USB_GADGET_DELAYED_STATUS to avoid compilation error
Added USB_GADGET_DELAYED_STATUS to avoid the following compilation error.
error: ‘USB_GADGET_DELAYED_STATUS’ undeclared (first use in this function)
while compiling dwc3/ep0.c

While this is been added only to avoid compilation error, the complete fix
should be something like the one added in linux kernel. The complete fix
will be ported once we have the composite driver in u-boot look similar to
the one in linux kernel.
commit 1b9ba000177ee47bcc5b44c7c34e48e735f5f9b1
Author: Roger Quadros <roger.quadros@nokia.com>
Date:   Mon May 9 13:08:06 2011 +0300

    usb: gadget: composite: Allow function drivers to pause control transfers

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
b6d959acaa usb: dwc3: ep0: make dwc3 ep0 build in uboot
*) Changed the included header files to that used in u-boot.
*) added dwc3_ep_event_string() used in ep0.c
*) Fixed other misc warnings

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
72e7c32fe4 include: asm: types: add resource_size_t type
Added resource_size_t type in order to get rid of the following
compilation error whiel building dwc3 gadget.
include/linux/ioport.h:19:2: error: unknown type name ‘resource_size_t’

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
747a0a5b38 usb: dwc3: gadget: make dwc3 gadget build in uboot
Did a bunch of things to get dwc3/gadget.c compile in u-boot without
build errors and warnings
*) Changed the included header files to that used in u-boot.
*) Used dma_alloc_coherent and dma_free_coherent APIs of u-boot
*) removed sg support
*) remove jiffies and used a simple while loop
*) removed irq support and added a function to call these interrupt handler.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
18be4cb151 usb: dwc3: linux-compat: Add header for dwc3 linux compatibiltiy
Added a header file to include various linux specific APIs like
pr_debug, WARN_ WARN_ON_ONCE etc.. in order to avoid compilation
error while building dwc3 driver.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
2f06693567 arm: asm: dma-mapping: added dma_free_coherent API
Added dma_free_coherent corresponding to the dma_alloc_coherent in
dma-mapping.h in order to free memory allocated using dma_alloc_coherent.
This API is used in dwc3 driver.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
027b6103cd usb: dwc3: remove pm related operations from dwc3 driver
Removed all pm related operations including pm_runtime APIs,
suspend/resume hooks as support for these are not present in u-boot.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
9848e5740a usb: dwc3: fix dwc3 header files
Changed the header files included in core.h and io.h to the u-boot header
files so that these files can be included in other dwc3 source files and
be compiled in uboot. Also added otg.h which has the defines for dr_mode.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
9de1115de7 usb: dwc3: remove trace_* APIs from dwc3 driver
Removed most of the trace_* APIs from dwc3 driver since tracepoints are not
supported in u-boot. Replaced some of the trace_* API with dev_dbg/dev/vdbg.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Review-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:09 +02:00
Kishon Vijay Abraham I
30c31d5897 usb: dwc3: Modify the file headers to u-boot format
Modified the file header to the format that is used in u-boot. Also
included in the header, the commit in linux kernel from which each of
these files are added.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
97798eb96d usb: dwc3: remove un-used files from dwc3 folder
removed un-used/un-supported files from dwc3. These files can be added
later as and when the support is added.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
85d5e7075f usb: dwc3: add dwc3 folder from linux kernel to u-boot
Added dwc3 folder from linux kernel 3.19-rc1 (97bf6af1f9)
to u-boot. This will be adapted to work with u-boot in the
following patches.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
aecbf87965 include: asm: dma-mapping: get rid of the compilation warning in udc-core
Fixed the following warning here.
"warning: ‘dma_alloc_coherent’ defined but not used" while compiling
udc-core

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
103fa06cfe usb: gadget: udc: make udc-core compile in u-boot build
Make udc-core compile in u-boot by removing all linux specific
stuff and having only the bare minimal udc-core required for
usb gadget drivers. Also modified the file header to a format that is
generally being used in u-boot.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
45d9337ec3 include: usb: modify gadget.h to include udc support
Made changes in gadget.h that is required after adding udc-core.c
except changes that might break other platforms.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
a139b96a47 usb: gadget: udc: add udc-core from linux kernel to u-boot
Added udc-core.c from linux kernel 3.19-rc1 (97bf6af1f9) to u-boot.
This will be adapted to work with u-boot in the
following patches.
Adding support for udc will help to seamlessly port dwc3 driver from
linux kernel to u-boot (since dwc3 uses udc-core) and it'll also help
to add support for multiple gadget controllers to be functional at the
same time.
All other gadget drivers can also be adapted to use udc-core.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
fc2f15d2f7 ARM: AM43xx: Enable clocks for USB OTGSS and USB PHY
Enabled clocks for dwc3 controller and USB PHY present in AM43xx.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Kishon Vijay Abraham I
d3cfcb3e2c ARM: DRA7: Enable clocks for USB OTGSS and USB PHY
Enabled clocks for dwc3 controller and USB PHY present in DRA7.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
2015-04-14 05:48:08 +02:00
Stephen Warren
5877de9165 usb: dwc2: retry NAK'd interrupt transfers
IIUC, interrupt transfers are NAK'd by devices until they wish to trigger
an interrupt, and e.g. EHCI controllers retry these in HW until they are
ACK'd. However, DWC2 doesn't seem to retry, so we need to do this in SW.
In practice, I've seen DWC2_HCINT_FRMOVRUN happen too. I'm not quite sure
what this error implies; perhaps it's related to how near the end of a
USB frame we're at when the interrupt transfer is initiated? Anyway,
retrying this temporary error seems to be necessary too.

With all these commits applied, both my USB keyboards (one LS Lenovo and
one FS Dell) work correctly when there is no USB hub between the SoC and
the keyboard; We still need split transactions to be implemented for hubs
to work.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
e236519b73 usb: dwc2: implement interrupt transfers
As best I can tell, there's no difference between bulk and interrupt
transfers in terms of how the HW should be programmed, at least given
that we're executing one transaction at a time rather than scheduling
them into frames for maximum throughput.

This patch ends up sharing the toggle bit state between bulk and
interrupt transfers on a particular EP. However I believe this is fine;
AFAIK a given EP either uses bulk or interrupt transfers and doesn't mix
them.

This patch doesn't do anything with the "interval" parameter for
interrupt transfers, but then most other USB controller drivers in U-Boot
don't either.

It turns out that one of my keyboards is happy to work using control
transfers but the other only gives non-zero "HID reports" via interrupt
transfers.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
ed9bcbc792 usb: dwc2: correctly program hcchar for LS devices
A bit must be set in HCCHAR when communicating with low-speed devices.
I have no idea why there's no corresponding bit to distinguish between
full-speed and high-speed devices, but no matter; they all work now!

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
122426d46e ARM: bcm2835: use phys_to_bus() for mbox
When we communicate with the VideoCore to perform property mailbox
transactions, that is a DMA operation as far as the property buffer
is concerned. Use phys_to_bus() on that buffer.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
4748cce573 usb: dwc2: detect device speed correctly
This doesn't make my LS keyboard work any better, but it does at least
report the correct speed in "usb tree".

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
5c0beb5c58 usb: dwc2: use phys_to_bus/bus_to_phys
Use of these APIs is required on the Raspberry Pi. With this change, USB
on RPi1 should be more reliable, and USB on the RPi2 will start working.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
79340db7f1 ARM: bcm2835: implement phys_to_bus/bus_to_phys
The BCM283[56] contain both a L1 and L2 cache between the GPU (a/k/a
VideoCore CPU?) and DRAM. DMA-capable peripherals can also optionally
access DRAM via this same  L2 cache (although they always bypass the L1
cache). Peripherals select whether to use or bypass the cache via the
top two bits of the bus address.

An IOMMU exists between the ARM CPU and the rest of the system. This
controls whether the ARM CPU's accesses use or bypass the L1 and/or L2
cache. This IOMMU is configured/controlled exclusively by the VideoCore
CPU.

In order for DRAM accesses made by the ARM core to be coherent with
accesses made by other DMA peripherals, we must program a bus address
into those peripherals that causes the peripheral's accesses to use the
same set of caches that the ARM core's accesses will use.

On the RPi1, the VideoCore firmware sets up the IOMMU to enable use of
the L2 cache. This corresponds to addresses based at 0x40000000.

On the RPi2, the VideoCore firmware sets up the IOMMU to disable use of
the L2 cache. This corresponds to addresses based at 0xc0000000.

This patch implements U-Boot's phys_to_bus/bus_to_phys APIs according
to those rules.

For full details of this setup, please see Dom Cobley's description at:
http://lists.denx.de/pipermail/u-boot/2015-March/208201.html
http://permalink.gmane.org/gmane.comp.boot-loaders.u-boot/215038
https://www.mail-archive.com/u-boot@lists.denx.de/msg166568.html

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
927c1fa266 Create API to map between CPU physical and bus addresses
On some SoCs, DMA-capable peripherals see a different address space to
the CPU's physical address space. Create an API to allow platform-agnostic
drivers to convert between the two address spaces when programming DMA
operations.

This API will exist on all platforms, but will have a dummy implementation
when this feature is not required. Other platforms will enable
CONFIG_PHYS_TO_BUS and provide the required implementation.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
fc909c0563 usb: dwc2: fix bulk transfers
When I created wait_for_chhltd(), I noticed that some instances of the
code it replaced expected the ACK bit to be set and others didn't. I
assumed this was an accidental inconsistency in the code, so wrote
wait_for_chhltd() to always expect ACK to be set. This code appeared to
work correctly for both enumeration of USB keyboards and operation of
USB Ethernet devices. However, this change broke USB Mass Storage (at
least my USB SD card reader). This change reverts to exactly the
original behaviour. I'm not sure why the ACK bit isn't always set
(perhaps a quirk in the USB HW or DWC2 controller), but the code works
this way!

Fixes: 5be4ca7d6ac8 ("usb: dwc2: unify waiting for transfer completion")
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
805b67e1ea usb: dwc2: remove restriction on buffer length
Each USB transfer is split up into chunks that are held in an aligned
buffer. This imposes a limit on the size of each chunk, but no limit on
the total size of transferred data. Fix the logic in chunk_msg() not to
reject large transfers, but simply take the size of the aligned buffer
into account when calculating the chunk size.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
d1c880c66c usb: dwc2: fix aligned buffer usage
The original aligned_buffer usage:
a) Uselessly copied data into the aligned buffer even for IN
   transactions. Fix this my making the copy conditional.
b) Always programmed the HW to transfer to/from the start of the aligned
   buffer. This worked fine for OUT transactions since the memcpy copied
   the OUT data to this location too. However, for large IN transactions,
   since the copy from the aligned buffer to the "client" buffer was
   deferred until after all chunks were transferred. it resulted in each
   chunk's transfer over-writing the data for the first transfer. Fix
   this by copying IN data as soon as it's received.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:59 +02:00
Stephen Warren
66ffc87586 usb: dwc2: simplify wait_for_chhltd
toggle is never NULL. Simplify the code by removing handling of when it
is NULL.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:58 +02:00
Stephen Warren
282685e07e usb: dwc2: remove control_data_toggle[]
The control data toggle resets to DATA1 at the start of the data phase
of every setup transaction. We don't need a global variable to store
the value; we can just store it on the stack.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:58 +02:00
Stephen Warren
ee83755401 usb: dwc2: usb chunk_msg() for control transfers too
This removes duplicated code.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:58 +02:00
Stephen Warren
7b5e504dae usb: dwc2: refactor submit_bulk_msg to be common
Move the body of submit_bulk_msg() into new function chunk_msg(). This
can be shared with submit_control_msg() to reduce code duplication, and
allow control messages larger than maxpacket.

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:58 +02:00
Stephen Warren
4a1d21fc52 usb: dwc2: unify waiting for transfer completion
Lift common code out of submit_bulk_msg() and submit_control_msg().

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:58 +02:00
Tim Harvey
319418c01c usb: hub: allow pgood_delay to be specified via env
Some USB devices break the spec and require longer warm-up times. Allow
the usb_pgood_delay env variable to override the calculated time.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
2015-04-14 05:47:48 +02:00
Stephen Warren
25c0673635 usb: fix first descriptor fetch error handling
When fetching the first descriptor from a new device, only validate that
we received at least 8 bytes, not that we received the entire descriptor.
The reasoning is:
- The code only uses fields in the first 8 bytes, so that's all we need
  to have fetched at this stage.
- The smallest maxpacket size is 8 bytes. Before we know the actual
  maxpacket the device uses, the USB controller may only accept a single
  packet (see the DWC2 note in the comment added in the commit).
  Consequently we are only guaranteed to receive 1 packet (at least 8
  bytes) even in a non-error case.

Fixes: 1a7758044b04 ("usb: Early failure when the first descriptor read
fails or is invalid")
Cc: Paul Kocialkowski <contact@paulk.fr>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
2015-04-14 05:47:48 +02:00