Re: [PATCH] drm/bridge/synopsys: dsi: Don't blindly call post_disable

[Matt Redfearn]

Hi Andrzej,

On 25/04/2019 13:13, Andrzej Hajda wrote:
> On 24.04.2019 16:22, Matt Redfearn wrote:
>> The DRM documentation states that post_disable is an optional callback.
>> As such an implementing device may not populate it. To avoid panicing
>> the kernel by calling a NULL function pointer, we should NULL check it
>> before blindy calling it.
>>
>> Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxxxx>
> 
>> ---
>>
>>   drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> index 38e88071363..0ee440216b8 100644
>> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>> @@ -805,7 +805,8 @@ static void dw_mipi_dsi_bridge_post_disable(struct drm_bridge *bridge)
>>   	 * This needs to be fixed in the drm_bridge framework and the API
>>   	 * needs to be updated to manage our own call chains...
>>   	 */
>> -	dsi->panel_bridge->funcs->post_disable(dsi->panel_bridge);
>> +	if (dsi->panel_bridge->funcs->post_disable)
>> +		dsi->panel_bridge->funcs->post_disable(dsi->panel_bridge);
>>   
> 
> Why not drm_bridge_post_disable ?

Ah - that seems like a nicer fix! Do you think the comment above 
describing why this function pointer is called directly can be removed 
as well if we go this route?

If someone calls drm_bridge_post_disable() on the Synposys DSI 
drm_bridge it will go on to call post_disable on all other bridges in 
the chain, in addition to us calling them here. Is it an issue to call 
it multiple times?

Thanks,
Matt


> 
> 
> Regards
> 
> Andrzej
> 
> 
>>   	if (dsi->slave) {
>>   		dw_mipi_dsi_disable(dsi->slave);
> 
>