From: "Tobias Jakobi (Compleo)" <tobias.jakobi.compleo@xxxxxxxxx> [ 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/ProductDocuments/Errata/KSZ87xx-Errata-DS80000687C.pdf Signed-off-by: Tobias Jakobi (Compleo) <tobias.jakobi.compleo@xxxxxxxxx> Reviewed-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> Fixes: 7b6e6235b664 ("net: dsa: microchip: ksz8795: handle eee specif erratum") Link: https://lore.kernel.org/r/20240304154135.161332-1-tobias.jakobi.compleo@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 91aba470fb2fa..28d7ada3ec067 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); -- 2.43.0
