From: "Tobias Jakobi (Compleo)" <[email protected]>
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) <[email protected]>
---
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 61b71bcfe396..c3da97abce20 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);
--
2.34.1
On Mon, Mar 04, 2024 at 04:41:35PM +0100, [email protected] wrote:
> From: "Tobias Jakobi (Compleo)" <[email protected]>
>
> 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) <[email protected]>
The subject should have [PATCH net] for stable and Fixes tag:
Fixes: 7b6e6235b664 ("net: dsa: microchip: ksz8795: handle eee specif erratum")
Reviewed-by: Oleksij Rempel <[email protected]>
Thank you!
Regards,
Oleksij
--
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Steuerwalder Str. 21 | http://www.pengutronix.de/ |
31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
Hello:
This patch was applied to netdev/net.git (main)
by Jakub Kicinski <[email protected]>:
On Mon, 4 Mar 2024 16:41:35 +0100 you wrote:
> From: "Tobias Jakobi (Compleo)" <[email protected]>
>
> 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].
>
> [...]
Here is the summary with links:
- net: dsa: microchip: fix register write order in ksz8_ind_write8()
https://git.kernel.org/netdev/net/c/b7fb7729c94f
You are awesome, thank you!
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