linux-kernel - Re: [PATCH v2] drm/xe/hwmon: Return early on power limit read failure

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Message-ID: <aKIBNeuupayX6awq@intel.com>
Date: Sun, 17 Aug 2025 12:20:05 -0400
From: Rodrigo Vivi <rodrigo.vivi@...el.com>
To: <zhaoguohan@...inos.cn>
CC: <lucas.demarchi@...el.com>, <thomas.hellstrom@...ux.intel.com>,
	<airlied@...il.com>, <simona@...ll.ch>, <badal.nilawar@...el.com>,
	<karthik.poosa@...el.com>, <riana.tauro@...el.com>, "open list:INTEL DRM XE
 DRIVER (Lunar Lake and newer)" <intel-xe@...ts.freedesktop.org>, "open
 list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>, open list
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/xe/hwmon: Return early on power limit read failure

On Fri, Aug 15, 2025 at 02:36:23PM +0800, zhaoguohan@...inos.cn wrote:
> From: GuoHan Zhao <zhaoguohan@...inos.cn>
> 
> In xe_hwmon_pcode_rmw_power_limit(), when xe_pcode_read() fails,
> the function logs the error but continues to execute the subsequent
> logic. This can result in undefined behavior as the values val0 and
> val1 may contain invalid data.
> 
> Fix this by adding an early return after logging the read failure,
> ensuring that we don't proceed with potentially corrupted data.
> 
> Fixes: 8aa7306631f0 ("drm/xe/hwmon: Fix xe_hwmon_power_max_write")
> 
> V2:
> - Change 'drm_dbg' to 'drm_err'
> - Added the Fixes tag in commit message

There are still missed/unanswered questions/concerns in the original review:

https://lore.kernel.org/intel-xe/aJtG0xmBBgwnTANg@intel.com

Please ensure to address all of them before re-iterating the patch.

Thanks,
Rodrigo.

> 
> Signed-off-by: GuoHan Zhao <zhaoguohan@...inos.cn>
> ---
>  drivers/gpu/drm/xe/xe_hwmon.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
> index f08fc4377d25..8e29fa155d7e 100644
> --- a/drivers/gpu/drm/xe/xe_hwmon.c
> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
> @@ -190,9 +190,11 @@ static int xe_hwmon_pcode_rmw_power_limit(const struct xe_hwmon *hwmon, u32 attr
>  						  READ_PL_FROM_PCODE : READ_PL_FROM_FW),
>  						  &val0, &val1);
>  
> -	if (ret)
> -		drm_dbg(&hwmon->xe->drm, "read failed ch %d val0 0x%08x, val1 0x%08x, ret %d\n",
> +	if (ret) {
> +		drm_err(&hwmon->xe->drm, "read failed ch %d val0 0x%08x, val1 0x%08x, ret %d\n",
>  			channel, val0, val1, ret);
> +		return ret;
> +	}
>  
>  	if (attr == PL1_HWMON_ATTR)
>  		val0 = (val0 & ~clr) | set;
> -- 
> 2.43.0
>