Re: [PATCH] drm/msm/dsi: add protection against NULL dsi device

[Abhinav Kumar <abhinavk@codeaurora.org>]

On 2019-03-07 13:59, Sean Paul wrote:
> On Wed, Mar 06, 2019 at 05:28:54PM -0800, Abhinav Kumar wrote:
>> When panel probe happens after DSI probe, the DSI probe
>> is deferred as per current design. In the probe defer path
>> dsi device is destroyed. This NULL dsi device could be
>> deferenced by the panel probe in the mipi_dsi_attach path.
>> 
>> Check for NULL dsi device before accessing it.
> 
> It would be really nice to sort all of this out in a manner that's not
> sprinkling NULL checks around the driver. I spent 5 minutes looking 
> around and
> couldn't really make sense of how all of these pieces interact, but 
> this seems
> like it might be an architectural problem (perhaps since dpu was using 
> its own
> panel stuff instead of drm_panel?).
> 
> Anyways, it'd be nice to fix that.
> 
> In the meantime, could you please add a big comment like the !dev check 
> in this
> function explaining how this situation can come to pass? That way the 
> knowledge
> isn't lost and whoever comes along to clean up all of these probe 
> checks will
> have some clue as to what's going on.
> 
> Sean
[Abhinav] Sure Sean, will add a detailed comment to explain the scenario
> 
>> 
>> Reported-by: Jeffrey Hugo <jhugo@codeaurora.org>
>> Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
>> Signed-off-by: Abhinav Kumar <abhinavk@codeaurora.org>
>> ---
>>  drivers/gpu/drm/msm/dsi/dsi_manager.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> index 80aa634..cc2569d 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>> @@ -769,7 +769,7 @@ bool msm_dsi_manager_cmd_xfer_trigger(int id, u32 
>> dma_base, u32 len)
>>  void msm_dsi_manager_attach_dsi_device(int id, u32 device_flags)
>>  {
>>  	struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>> -	struct drm_device *dev = msm_dsi->dev;
>> +	struct drm_device *dev = msm_dsi ? msm_dsi->dev : NULL;
>>  	struct msm_drm_private *priv;
>>  	struct msm_kms *kms;
>>  	struct drm_encoder *encoder;
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
>> Forum,
>> a Linux Foundation Collaborative Project
>> 
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