linux-kernel - Re: [PATCH v3] drm/dp_mst: Fix return code on sideband message failure

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Date:   Tue, 13 Jul 2021 15:24:58 -0700
From:   khsieh@...eaurora.org
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     robdclark@...il.com, sean@...rly.run, swboyd@...omium.org,
        lyude@...hat.com, abhinavk@...eaurora.org, aravindh@...eaurora.org,
        rsubbia@...eaurora.org, rnayak@...eaurora.org,
        freedreno@...ts.freedesktop.org, airlied@...ux.ie, daniel@...ll.ch,
        maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] drm/dp_mst: Fix return code on sideband message
 failure

On 2021-07-07 01:37, Jani Nikula wrote:
> On Tue, 06 Jul 2021, Kuogee Hsieh <khsieh@...eaurora.org> wrote:
>> From: Rajkumar Subbiah <rsubbia@...eaurora.org>
>> 
>> Commit 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing +
>> selftests") added some debug code for sideband message tracing. But
>> it seems to have unintentionally changed the behavior on sideband 
>> message
>> failure. It catches and returns failure only if DRM_UT_DP is enabled.
>> Otherwise it ignores the error code and returns success. So on an MST
>> unplug, the caller is unaware that the clear payload message failed 
>> and
>> ends up waiting for 4 seconds for the response. Fixes the issue by
>> returning the proper error code.
>> 
>> Changes in V2:
>> -- Revise commit text as review comment
>> -- add Fixes text
>> 
>> Changes in V3:
>> -- remove "unlikely" optimization
>> 
>> Fixes: 2f015ec6eab6 ("drm/dp_mst: Add sideband down request tracing + 
>> selftests")
>> 
>> Signed-off-by: Rajkumar Subbiah <rsubbia@...eaurora.org>
>> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
>> 
>> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> 
> Reviewed-by: Jani Nikula <jani.nikula@...el.com>
> 
> 
>> ---
Lyude,
Any comments from you?
Thanks,

>>  drivers/gpu/drm/drm_dp_mst_topology.c | 10 ++++++----
>>  1 file changed, 6 insertions(+), 4 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c 
>> b/drivers/gpu/drm/drm_dp_mst_topology.c
>> index 1590144..df91110 100644
>> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
>> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
>> @@ -2887,11 +2887,13 @@ static int process_single_tx_qlock(struct 
>> drm_dp_mst_topology_mgr *mgr,
>>  	idx += tosend + 1;
>> 
>>  	ret = drm_dp_send_sideband_msg(mgr, up, chunk, idx);
>> -	if (unlikely(ret) && drm_debug_enabled(DRM_UT_DP)) {
>> -		struct drm_printer p = drm_debug_printer(DBG_PREFIX);
>> +	if (ret) {
>> +		if (drm_debug_enabled(DRM_UT_DP)) {
>> +			struct drm_printer p = drm_debug_printer(DBG_PREFIX);
>> 
>> -		drm_printf(&p, "sideband msg failed to send\n");
>> -		drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
>> +			drm_printf(&p, "sideband msg failed to send\n");
>> +			drm_dp_mst_dump_sideband_msg_tx(&p, txmsg);
>> +		}
>>  		return ret;
>>  	}