From: "Tobias Jakobi (Compleo)" tobias.jakobi.compleo@gmail.com
[ Upstream commit b7fb7729c94fb2d23c79ff44f7a2da089c92d81c ]
This bug was noticed while re-implementing parts of the kernel driver in userspace using spidev. The goal was to enable some of the errata workarounds that Microchip describes in their errata sheet [1].
Both the errata sheet and the regular datasheet of e.g. the KSZ8795 imply that you need to do this for indirect register accesses: - write a 16-bit value to a control register pair (this value consists of the indirect register table, and the offset inside the table) - either read or write an 8-bit value from the data storage register (indicated by REG_IND_BYTE in the kernel)
The current implementation has the order swapped. It can be proven, by reading back some indirect register with known content (the EEE register modified in ksz8_handle_global_errata() is one of these), that this implementation does not work.
Private discussion with Oleksij Rempel of Pengutronix has revealed that the workaround was apparantly never tested on actual hardware.
[1] https://ww1.microchip.com/downloads/aemDocuments/documents/OTH/ProductDocume...
Signed-off-by: Tobias Jakobi (Compleo) tobias.jakobi.compleo@gmail.com Reviewed-by: Oleksij Rempel o.rempel@pengutronix.de Fixes: 7b6e6235b664 ("net: dsa: microchip: ksz8795: handle eee specif erratum") Link: https://lore.kernel.org/r/20240304154135.161332-1-tobias.jakobi.compleo@gmai... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/net/dsa/microchip/ksz8795.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/net/dsa/microchip/ksz8795.c b/drivers/net/dsa/microchip/ksz8795.c index c63e082dc57dc..934600eccbaf2 100644 --- a/drivers/net/dsa/microchip/ksz8795.c +++ b/drivers/net/dsa/microchip/ksz8795.c @@ -49,9 +49,9 @@ static int ksz8_ind_write8(struct ksz_device *dev, u8 table, u16 addr, u8 data) mutex_lock(&dev->alu_mutex);
ctrl_addr = IND_ACC_TABLE(table) | addr; - ret = ksz_write8(dev, regs[REG_IND_BYTE], data); + ret = ksz_write16(dev, regs[REG_IND_CTRL_0], ctrl_addr); if (!ret) - ret = ksz_write16(dev, regs[REG_IND_CTRL_0], ctrl_addr); + ret = ksz_write8(dev, regs[REG_IND_BYTE], data);
mutex_unlock(&dev->alu_mutex);