linux-kernel - Re: [patch] drm/i915: fix a read size argument

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Date:   Thu, 13 Oct 2016 11:27:28 +0200
From:   walter harms <wharms@....de>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     Daniel Vetter <daniel.vetter@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [patch] drm/i915: fix a read size argument



Am 13.10.2016 10:55, schrieb Dan Carpenter:
> We want to read 3 bytes here, but because the parenthesis are in the
> wrong place we instead read:
> 
> 	sizeof(intel_dp->edp_dpcd) == sizeof(intel_dp->edp_dpcd)
> 
> which is one byte.
> 
> Fixes: fe5a66f91c88 ("drm/i915: Read PSR caps/intermediate freqs/etc. only once on eDP")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 14a3cf0..ee8aa95 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -3551,8 +3551,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
>  	/* Read the eDP Display control capabilities registers */
>  	if ((intel_dp->dpcd[DP_EDP_CONFIGURATION_CAP] & DP_DPCD_DISPLAY_CONTROL_CAPABLE) &&
>  	    drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
> -			     intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd) ==
> -			     sizeof(intel_dp->edp_dpcd)))
> +			     intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
> +			     sizeof(intel_dp->edp_dpcd))



perhaps we can morph that into something more readable ? I would suggest:


if (intel_dp->dpcd[DP_EDP_CONFIGURATION_CAP] & DP_DPCD_DISPLAY_CONTROL_CAPABLE)
  {
    size_t size=sizeof(intel_dp->edp_dpcd); /* == EDP_DISPLAY_CTL_CAP_SIZE */
    int ret;	

    ret=drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,intel_dp->edp_dpcd,size);	

    if (ret != size )
        ......

 }

this way it improves readability and reduces line length.


>  		DRM_DEBUG_KMS("EDP DPCD : %*ph\n", (int) sizeof(intel_dp->edp_dpcd),
>  			      intel_dp->edp_dpcd);
>  
> --
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