From: Marek Vasut marex@denx.de
[ Upstream commit 5ae06327a3a5bad4ee246d81df203b1b00a7b390 ]
The blamed commit has replaced a ksz_write8() call to address REG_PORT_5_CTRL_6 (0x56) with a ksz_set_xmii() -> ksz_pwrite8() call to regs[P_XMII_CTRL_1], which is also defined as 0x56 for ksz8795_regs[].
The trouble is that, when compared to ksz_write8(), ksz_pwrite8() also adjusts the register offset with the port base address. So in reality, ksz_pwrite8(offset=0x56) accesses register 0x56 + 0x50 = 0xa6, which in this switch appears to be unmapped, and the RGMII delay configuration on the CPU port does nothing.
So if the switch wasn't fine with the RGMII delay configuration done through pin strapping and relied on Linux to apply a different one in order to pass traffic, this is now broken.
Using the offset translation logic imposed by ksz_pwrite8(), the correct value for regs[P_XMII_CTRL_1] should have been 0x6 on ksz8795_regs[], in order to really end up accessing register 0x56.
Static code analysis shows that, despite there being multiple other accesses to regs[P_XMII_CTRL_1] in this driver, the only code path that is applicable to ksz8795_regs[] and ksz8_dev_ops is ksz_set_xmii(). Therefore, the problem is isolated to RGMII delays.
In its current form, ksz8795_regs[] contains the same value for P_XMII_CTRL_0 and for P_XMII_CTRL_1, and this raises valid suspicions that writes made by the driver to regs[P_XMII_CTRL_0] might overwrite writes made to regs[P_XMII_CTRL_1] or vice versa.
Again, static analysis shows that the only accesses to P_XMII_CTRL_0 from the driver are made from code paths which are not reachable with ksz8_dev_ops. So the accesses made by ksz_set_xmii() are safe for this switch family.
[ vladimiroltean: rewrote commit message ]
Fixes: c476bede4b0f ("net: dsa: microchip: ksz8795: use common xmii function") Signed-off-by: Marek Vasut marex@denx.de Signed-off-by: Vladimir Oltean vladimir.oltean@nxp.com Acked-by: Arun Ramadoss arun.ramadoss@microchip.com Reviewed-by: Florian Fainelli f.fainelli@gmail.com Link: https://lore.kernel.org/r/20230315231916.2998480-1-vladimir.oltean@nxp.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/dsa/microchip/ksz_common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c index 9b20c2ee6d62a..19cd05762ab77 100644 --- a/drivers/net/dsa/microchip/ksz_common.c +++ b/drivers/net/dsa/microchip/ksz_common.c @@ -310,7 +310,7 @@ static const u16 ksz8795_regs[] = { [S_BROADCAST_CTRL] = 0x06, [S_MULTICAST_CTRL] = 0x04, [P_XMII_CTRL_0] = 0x06, - [P_XMII_CTRL_1] = 0x56, + [P_XMII_CTRL_1] = 0x06, };
static const u32 ksz8795_masks[] = {