Some dwmac variants such as dwmac_socfpga don't use xpcs but lynx_pcs.

Don't call xpcs_config_eee_mult_fact() in this case, as this causes a
crash at init :

 Unable to handle kernel NULL pointer dereference at virtual address 00000039 when write

 [...]

 Call trace:
  xpcs_config_eee_mult_fact from stmmac_pcs_setup+0x40/0x10c
  stmmac_pcs_setup from stmmac_dvr_probe+0xc0c/0x1244
  stmmac_dvr_probe from socfpga_dwmac_probe+0x130/0x1bc
  socfpga_dwmac_probe from platform_probe+0x5c/0xb0

Fixes: 060fb27060e8 ("net: stmmac: call xpcs_config_eee_mult_fact()")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
This targets net-next as the blamed commit is also still in net-next.

 drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
index 7c0a4046bbe3..836f2848dfeb 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
@@ -524,7 +524,8 @@ int stmmac_pcs_setup(struct net_device *ndev)
 	if (ret)
 		return dev_err_probe(priv->device, ret, "No xPCS found\n");
 
-	xpcs_config_eee_mult_fact(xpcs, priv->plat->mult_fact_100ns);
+	if (xpcs)
+		xpcs_config_eee_mult_fact(xpcs, priv->plat->mult_fact_100ns);
 
 	priv->hw->xpcs = xpcs;
 
-- 
2.48.1

On Fri, Mar 21, 2025 at 11:35:01AM +0100, Maxime Chevallier wrote:
> Some dwmac variants such as dwmac_socfpga don't use xpcs but lynx_pcs.
> 
> Don't call xpcs_config_eee_mult_fact() in this case, as this causes a
> crash at init :
> 
>  Unable to handle kernel NULL pointer dereference at virtual address 00000039 when write
> 
>  [...]
> 
>  Call trace:
>   xpcs_config_eee_mult_fact from stmmac_pcs_setup+0x40/0x10c
>   stmmac_pcs_setup from stmmac_dvr_probe+0xc0c/0x1244
>   stmmac_dvr_probe from socfpga_dwmac_probe+0x130/0x1bc
>   socfpga_dwmac_probe from platform_probe+0x5c/0xb0
> 
> Fixes: 060fb27060e8 ("net: stmmac: call xpcs_config_eee_mult_fact()")
> Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>

Yes, I had noticed that but haven't had time to patch it, so thanks for
submitting the patch. However, I think the code structure could be
better in this function. Let's get the bug fixed, so:

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Thanks!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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