This is a note to let you know that I've just added the patch titled
net: dsa: microchip: fix register write order in ksz8_ind_write8()
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
net-dsa-microchip-fix-register-write-order-in-ksz8_i.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit dd3dc3fe3d65c71fab33f9c6fdb6fcae93938428
Author: Tobias Jakobi (Compleo) <tobias.jakobi.compleo@xxxxxxxxx>
Date: Mon Mar 4 16:41:35 2024 +0100
net: dsa: microchip: fix register write order in ksz8_ind_write8()
[ 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>
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);
