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[128.101.106.66]) by smtp.gmail.com with ESMTPSA id h23sm2569757ywc.105.2019.12.19.09.06.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2019 09:06:52 -0800 (PST) Subject: Re: [PATCH] drm/amd/display: replace BUG_ON with WARN_ON To: Mikita Lipski Cc: "David (ChunMing) Zhou" , Mario Kleiner , Leo Li , Bhawanpreet Lakha , David Francis , kjlu@umn.edu, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, Nicholas Kazlauskas , David Airlie , dri-devel@lists.freedesktop.org, Daniel Vetter , Alex Deucher , Harry Wentland , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20191218161505.13416-1-pakki001@umn.edu> From: Aditya Pakki In-Reply-To: Message-ID: Date: Thu, 19 Dec 2019 11:06:51 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/19 10:29 AM, Mikita Lipski wrote: > > > On 12/18/19 11:15 AM, Aditya Pakki wrote: >> In skip_modeset label within dm_update_crtc_state(), the dc stream >> cannot be NULL. Using BUG_ON as an assertion is not required and >> can be removed. The patch replaces the check with a WARN_ON in case >> dm_new_crtc_state->stream is NULL. >> >> Signed-off-by: Aditya Pakki >> --- >>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- >>   1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c >> index 7aac9568d3be..03cb30913c20 100644 >> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c >> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c >> @@ -7012,7 +7012,7 @@ static int dm_update_crtc_state(struct amdgpu_display_manager *dm, >>        * 3. Is currently active and enabled. >>        * => The dc stream state currently exists. >>        */ >> -    BUG_ON(dm_new_crtc_state->stream == NULL); >> +    WARN_ON(!dm_new_crtc_state->stream); >>   > > Thanks for the patch, but this is NAK from me since it doesn't really do anything to prevent it or fix it. > > If the stream is NULL and it passed this far in the function then something really wrong has happened and the process should be stopped. > > I'm currently dealing with an issue where dm_new_crtc_state->stream is NULL. One of the scenarios could be that driver creates stream for a fake sink instead of failing, that is connected over MST, and calls dm_update_crtc_state to enable CRTC. > >>       /* Scaling or underscan settings */ >>       if (is_scaling_state_different(dm_old_conn_state, dm_new_conn_state)) >> > Thanks Mikita for your advice regarding the patch. However, would a better error handling in this scenario be helpful ? Clearly, the stream variable is dereferenced in update_stream_scaling_settings would have the same impact as a crash ?