diff mbox series

net: dsa: microchip: fix register write order in ksz8_ind_write8()

Message ID 20240304154135.161332-1-tobias.jakobi.compleo@gmail.com (mailing list archive)
State Accepted
Commit b7fb7729c94fb2d23c79ff44f7a2da089c92d81c
Delegated to: Netdev Maintainers
Headers show
Series net: dsa: microchip: fix register write order in ksz8_ind_write8() | expand

Checks

Context Check Description
netdev/series_format warning Single patches do not need cover letters; Target tree name not specified in the subject
netdev/tree_selection success Guessed tree name to be net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 940 this patch: 940
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 9 of 9 maintainers
netdev/build_clang success Errors and warnings before: 956 this patch: 956
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 956 this patch: 956
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 11 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-03-05--21-00 (tests: 892)

Commit Message

tobias.jakobi.compleo@gmail.com March 4, 2024, 3:41 p.m. UTC 
From: "Tobias Jakobi (Compleo)" <tobias.jakobi.compleo@gmail.com>

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@gmail.com>
---
 drivers/net/dsa/microchip/ksz8795.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Oleksij Rempel March 5, 2024, 11:40 a.m. UTC | #1 
On Mon, Mar 04, 2024 at 04:41:35PM +0100, tobias.jakobi.compleo@gmail.com wrote:
> From: "Tobias Jakobi (Compleo)" <tobias.jakobi.compleo@gmail.com>
> 
> 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@gmail.com>

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 <o.rempel@pengutronix.de>

Thank you!
Regards,
Oleksij
patchwork-bot+netdevbpf@kernel.org March 6, 2024, 3:20 a.m. UTC | #2 
Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Mon,  4 Mar 2024 16:41:35 +0100 you wrote:
> From: "Tobias Jakobi (Compleo)" <tobias.jakobi.compleo@gmail.com>
> 
> 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!
diff mbox series

Patch

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);