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arm: mvebu: a38x: serdes: Add comments for hws_pex_config() code

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Add comments to understand what this magic code is doing.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Stefan Roese <sr@denx.de>
This commit is contained in:
Pali Rohár 2021-09-24 22:59:16 +02:00 committed by Stefan Roese
parent eb5d31645e
commit 2d5f51f680
1 changed files with 13 additions and 1 deletions
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14
arch/arm/mach-mvebu/serdes/a38x/ctrl_pex.c
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@ -42,6 +42,7 @@ int hws_pex_config(const struct serdes_map *serdes_map, u8 count)
continue;
}
/* Set Device/Port Type to RootComplex */
pex_idx = serdes_type - PEX0;
tmp = reg_read(PEX_CAPABILITIES_REG(pex_idx));
tmp &= ~(0xf << 20);
@ -122,12 +123,18 @@ int hws_pex_config(const struct serdes_map *serdes_map, u8 count)
}
next_busno++;
/*
* Read maximum link speed. It must be 0x2 (5.0 GT/s) as this
* value was set in serdes_power_up_ctrl() function.
*/
temp_pex_reg = reg_read((PEX_CFG_DIRECT_ACCESS
(pex_idx, PEX_LINK_CAPABILITY_REG)));
temp_pex_reg &= 0xf;
if (temp_pex_reg != 0x2)
continue;
/* Read negotiated link speed */
temp_reg = (reg_read(PEX_CFG_DIRECT_ACCESS(
pex_idx,
PEX_LINK_CTRL_STAT_REG)) &
@ -155,6 +162,7 @@ int hws_pex_config(const struct serdes_map *serdes_map, u8 count)
continue;
}
/* Find start of the PCI Express Capability registers */
while ((pex_config_read(pex_idx, first_busno, 0, 0, addr)
& 0xff) != 0x10) {
addr = (pex_config_read(pex_idx, first_busno, 0,
@ -173,11 +181,15 @@ int hws_pex_config(const struct serdes_map *serdes_map, u8 count)
tmp = reg_read(PEX_LINK_CTRL_STATUS2_REG(pex_idx));
DEBUG_RD_REG(PEX_LINK_CTRL_STATUS2_REG(pex_idx), tmp);
tmp &= ~(BIT(0) | BIT(1));
tmp |= BIT(1);
tmp |= BIT(1); /* Force Target Link Speed to 5.0 GT/s */
tmp |= BIT(6); /* Select Deemphasize (-3.5d_b) */
reg_write(PEX_LINK_CTRL_STATUS2_REG(pex_idx), tmp);
DEBUG_WR_REG(PEX_LINK_CTRL_STATUS2_REG(pex_idx), tmp);
/*
* Enable Auto Speed change. When set, link will issue link
* speed change to max possible link speed.
*/
tmp = reg_read(PEX_CTRL_REG(pex_idx));
DEBUG_RD_REG(PEX_CTRL_REG(pex_idx), tmp);
tmp |= BIT(10);