linux-kernel - Re: [PATCH] drm/bridge: anx7625: check the return on anx7625_aux

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Date:   Tue, 8 Mar 2022 17:45:41 -0800
From:   Tom Rix <trix@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     andrzej.hajda@...el.com, narmstrong@...libre.com,
        robert.foss@...aro.org, laurent.pinchart@...asonboard.com,
        jonas@...boo.se, jernej.skrabec@...il.com, airlied@...ux.ie,
        daniel@...ll.ch, nathan@...nel.org, xji@...logixsemi.com,
        sam@...nborg.org, tzungbi@...gle.com, pihsun@...omium.org,
        maxime@...no.tech, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        hsinyi@...omium.org
Subject: Re: [PATCH] drm/bridge: anx7625: check the return on
 anx7625_aux_trans


On 3/8/22 2:57 PM, Nick Desaulniers wrote:
> On Thu, Mar 3, 2022 at 12:19 PM <trix@...hat.com> wrote:
>> From: Tom Rix <trix@...hat.com>
>>
>> Clang static analysis reports this issue
>> anx7625.c:876:13: warning: The left operand of '&' is
>>    a garbage value
>>    if (!(bcap & 0xOA01)) {
>>          ~~~~ ^
>>
>> bcap is only set by a successful call to
>> anx7625_aux_trans().  So check.
>>
>> Fixes: cd1637c7e480 ("drm/bridge: anx7625: add HDCP support")
> Is this the correct Fixes tag?
yes
> I think it should be
>
> Fixes: adca62ec370c ("drm/bridge: anx7625: Support reading edid
> through aux channel")

This one changes the name of the function

-       anx7625_aux_dpcd_trans(ctx, DP_AUX_NATIVE_READ, 0x68028, 1, &bcap);
+       anx7625_aux_trans(ctx, DP_AUX_NATIVE_READ, 0x68028, 1, &bcap);

A return check from the earlier commit, when this block of code came 
into existence, is when it was first needed.

Tom

>
> instead.
>
>> Signed-off-by: Tom Rix <trix@...hat.com>
>> ---
>>   drivers/gpu/drm/bridge/analogix/anx7625.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
>> index 633618bafd75d..f02ac079ed2ec 100644
>> --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
>> +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
>> @@ -872,7 +872,10 @@ static int anx7625_hdcp_enable(struct anx7625_data *ctx)
>>          }
>>
>>          /* Read downstream capability */
>> -       anx7625_aux_trans(ctx, DP_AUX_NATIVE_READ, 0x68028, 1, &bcap);
>> +       ret = anx7625_aux_trans(ctx, DP_AUX_NATIVE_READ, 0x68028, 1, &bcap);
>> +       if (ret < 0)
>> +               return ret;
>> +
>>          if (!(bcap & 0x01)) {
>>                  pr_warn("downstream not support HDCP 1.4, cap(%x).\n", bcap);
>>                  return 0;
>> --
>> 2.26.3
>>
>