linux-kernel - Re: [PATCH] drm/bridge/synopsys: dsi: Don't blindly call post

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Message-ID: <95c36782-7eaf-2224-bb52-cff0a53d98d8@thinci.com>
Date:   Thu, 25 Apr 2019 12:39:27 +0000
From:   Matt Redfearn <matt.redfearn@...nci.com>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Philippe Cornu <philippe.cornu@...com>
CC:     "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Matthew Redfearn <matthew.redfearn@...nci.com>,
        Nickey Yang <nickey.yang@...k-chips.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Archit Taneja <architt@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/bridge/synopsys: dsi: Don't blindly call post_disable

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@...nci.com>
> 
>> ---
>>
>>   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);
> 
>