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u-boot/drivers/serial
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Rasmus Villemoes e698608680 serial: fix circular rx buffer edge case 
The current implementation of the circular rx buffer falls into a
common trap with circular buffers: It keeps the head/tail indices
reduced modulo the buffer size. The problem with that is that it makes
it impossible to distinguish "buffer full" from "buffer empty",
because in both situations one has head==tail.

This can easily be demonstrated: Build sandbox with RX_BUFFER enabled,
set the RX_BUFFER_SIZE to 32, and try pasting the string

  01234567890123456789012345678901

Nothing seems to happen, but in reality, all characters have been read
and put into the buffer, but then tstc ends up believing nothing is in
the buffer anyway because upriv->rd_ptr == upriv->wr_ptr.

A better approach is to let the indices be free-running, and only
reduce them modulo the buffer size when accessing the array. Then
"empty" is head-tail==0 and "full" is head-tail==size. This does rely
on the buffer size being a power-of-two and the free-running
indices simply wrapping around to 0 when incremented beyond the
maximal positive value.

Incidentally, that change from signed to unsigned int also improves
code generation quite a bit: In C, (signed int)%(signed int) is
defined to have the sign of the dividend (so (-35) % 32 is -3, not
29), and hence despite the modulus being a power-of-two, x % 32 does
not actually compile to the same as a simple x & 31 - on x86 with -Os,
it seems that gcc ends up emitting an idiv instruction, which is quite
expensive.

Signed-off-by: Rasmus Villemoes <ravi@prevas.dk>
Reviewed-by: Simon Glass <sjg@chromium.org>
2024-10-16 15:54:31 -06:00
..
altera_jtag_uart.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
altera_uart.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
arm_dcc.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
atmel_usart.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
atmel_usart.h SPDX: Convert all of our single license tags to Linux Kernel style 2018-05-07 09:34:12 -04:00
Kconfig serial: Support debug UART in TPL 2024-10-03 11:52:16 -06:00
Makefile drivers: serial: Add xtensa semihosting driver 2024-07-04 16:08:37 -06:00
ns16550.c arm: ti: Remove omap4 platform support 2024-07-23 10:37:48 -06:00
sandbox.c sandbox: Drop video-sync in serial driver 2024-07-31 16:56:06 +02:00
serial-uclass.c serial: fix circular rx buffer edge case 2024-10-16 15:54:31 -06:00
serial.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_adi_uart4.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_ar933x.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_arc.c drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
serial_bcm283x_mu.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_bcm283x_pl011.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_bcm6345.c treewide: Remove clk_free 2024-01-29 22:35:02 -05:00
serial_coreboot.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_cortina.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_efi.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_htif.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_intel_mid.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_linflexuart.c drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
serial_lpuart.c drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
serial_mcf.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_meson.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_mpc8xx.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_msm.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_msm_geni.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_mt7620.c cyclic: Use schedule() instead of WATCHDOG_RESET() 2022-09-18 10:26:33 +02:00
serial_mtk.c serial: mediatek: add special handling for highspeed and linux compat 2024-07-08 11:45:50 -06:00
serial_mvebu_a3700.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_mxc.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_mxs.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_npcm.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_ns16550.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_nulldev.c drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
serial_octeon_bootcmd.c cyclic: Use schedule() instead of WATCHDOG_RESET() 2022-09-18 10:26:33 +02:00
serial_octeon_pcie_console.c cyclic: Use schedule() instead of WATCHDOG_RESET() 2022-09-18 10:26:33 +02:00
serial_omap.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_owl.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_pic32.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_pl01x.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_pl01x_internal.h drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
serial_rockchip.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_s5p.c serial: s5p: Add Exynos850 compatible 2024-01-24 11:23:20 +09:00
serial_s5p4418_pl011.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_sbi.c serial: move sbi_dbcn_available to .data section 2024-03-12 14:36:13 +08:00
serial_semihosting.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_sh.c serial: sh: Drop <common.h> 2023-11-02 11:30:18 +01:00
serial_sh.h serial: sh: Add RZ/G2L SCIF support 2023-10-19 17:03:20 +02:00
serial_sifive.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_sti_asc.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_stm32.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_stm32.h serial: stm32: Fix AARCH64 compilation warnings 2023-11-13 10:55:38 +01:00
serial_uniphier.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_xen.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_xtensa_semihosting.c drivers: serial: Add xtensa semihosting driver 2024-07-04 16:08:37 -06:00
serial_xuartlite.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
serial_zynq.c Restore patch series "arm: dts: am62-beagleplay: Fix Beagleplay Ethernet" 2024-05-20 13:35:03 -06:00
usbtty.c drivers: serial: Remove duplicate newlines 2024-07-22 10:53:06 -06:00
usbtty.h global: Finish CONFIG -> CFG migration 2023-01-20 12:27:24 -05:00