[PATCH v2] net: dsa: realtek: rtl8365mb: fix mode mask calculation

[PATCH v2] net: dsa: realtek: rtl8365mb: fix mode mask calculation

[Mieczyslaw Nalewaj]

The RTL8365MB_DIGITAL_INTERFACE_SELECT_MODE_MASK macro was shifting
the 4-bit mask (0xF) by only (_extint % 2) bits instead of
(_extint % 2) * 4. This caused the mask to overlap with the adjacent
nibble when configuring odd-numbered external interfaces, selecting
the wrong bits entirely.

Align the shift calculation with the existing ...MODE_OFFSET macro.

Fixes: 4af2950c50c8 ("net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC")
Signed-off-by: Abdulkader Alrezej <alrazj.abdulkader@gmail.com>
Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Reviewed-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/net/dsa/realtek/rtl8365mb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/realtek/rtl8365mb.c
index ad7044b295ec..b85c99216648 100644
--- a/drivers/net/dsa/realtek/rtl8365mb.c
+++ b/drivers/net/dsa/realtek/rtl8365mb.c
@@ -216,7 +216,7 @@
 		 (_extint) == 2 ? RTL8365MB_DIGITAL_INTERFACE_SELECT_REG1 : \
 		 0x0)
 #define   RTL8365MB_DIGITAL_INTERFACE_SELECT_MODE_MASK(_extint) \
-		(0xF << (((_extint) % 2)))
+		(0xF << (((_extint) % 2) * 4))
 #define   RTL8365MB_DIGITAL_INTERFACE_SELECT_MODE_OFFSET(_extint) \
 		(((_extint) % 2) * 4)
 
-- 
2.53.0

Re: [PATCH v2] net: dsa: realtek: rtl8365mb: fix mode mask calculation

[Luiz Angelo Daros de Luca]

> The RTL8365MB_DIGITAL_INTERFACE_SELECT_MODE_MASK macro was shifting
> the 4-bit mask (0xF) by only (_extint % 2) bits instead of
> (_extint % 2) * 4. This caused the mask to overlap with the adjacent
> nibble when configuring odd-numbered external interfaces, selecting
> the wrong bits entirely.
>
> Align the shift calculation with the existing ...MODE_OFFSET macro.
>
> Fixes: 4af2950c50c8 ("net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC")
> Signed-off-by: Abdulkader Alrezej <alrazj.abdulkader@gmail.com>
> Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
> Reviewed-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>

This bug specifically affected ext1 (Port 6) for all digital interface
modes except DISABLED (0x0) and RGMII (0x1).

The error caused the mask for ext1 to overlap with the adjacent nibble
of ext0. Since ext0 is currently unused by all supported devices in
this family, the incorrect mask was zeroing bits that were already
expected to be zero, masking the failure.

However, for ext1, the incorrect shift left the effective mask with
only a single bit (bit 4) instead of the full 4-bit nibble (bits 4-7).
This meant the driver could only successfully write values 0x0 or 0x1.
Any mode requiring bits [7:5] (such as MII, RMII, or HSGMII) would
have been effectively written as 0x0 or 0x1, breaking those
configurations.

The original chip for this driver, RTL8365MB-VC, does utilize ext1,
but as the driver currently only implements RGMII mode, the hardware
result remained coincidentally correct:

Before patch: (0x0001 << 4) & 0x001E = 0x0010
After patch: (0x0001 << 4) & 0x00F0 = 0x0010

Tests on my device, TP-Link Archer C5v4, show no problem before and no
regressions, as ext1/port6 is not connected on that specific hardware.

Backporting note: There is no strict need to backport this fix to
stable trees, as only the RGMII mode was actually implemented and it
happened to work despite the logical error.

Regards,

Luiz

Re: [PATCH v2] net: dsa: realtek: rtl8365mb: fix mode mask calculation

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Sun, 19 Apr 2026 21:37:07 +0200 you wrote:
> The RTL8365MB_DIGITAL_INTERFACE_SELECT_MODE_MASK macro was shifting
> the 4-bit mask (0xF) by only (_extint % 2) bits instead of
> (_extint % 2) * 4. This caused the mask to overlap with the adjacent
> nibble when configuring odd-numbered external interfaces, selecting
> the wrong bits entirely.
> 
> Align the shift calculation with the existing ...MODE_OFFSET macro.
> 
> [...]

Here is the summary with links:
  - [v2] net: dsa: realtek: rtl8365mb: fix mode mask calculation
    https://git.kernel.org/netdev/net/c/0c078021d386

You are awesome, thank you!
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