linux-kernel - Re: [PATCH v5 2/6] drm: lcdif: Drop unnecessary NULL pointer check on lcdif->bridge

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Message-ID: <c9dedb24-5714-0301-d8cc-7c56673b07b0@denx.de>
Date:   Wed, 10 May 2023 10:40:35 +0200
From:   Marek Vasut <marex@...x.de>
To:     Ying Liu <gnuiyl@...il.com>
Cc:     Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, conor+dt@...nel.org,
        alexander.stein@...tq-group.com, shawnguo@...nel.org,
        s.hauer@...gutronix.de, krzysztof.kozlowski@...aro.org,
        robh+dt@...nel.org, linux-imx@....com,
        krzysztof.kozlowski+dt@...aro.org, kernel@...gutronix.de,
        LW@...o-electronics.de
Subject: Re: [PATCH v5 2/6] drm: lcdif: Drop unnecessary NULL pointer check on
 lcdif->bridge

On 5/10/23 10:30, Ying Liu wrote:
> On Tue, May 9, 2023 at 10:14 AM Marek Vasut <marex@...x.de> wrote:
>>
>> On 5/8/23 07:57, Liu Ying wrote:
>>
>> Hi,
> 
> Hi,

Hi,

>>> diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
>>> index 262bc43b1079..e54200a9fcb9 100644
>>> --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
>>> +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
>>> @@ -394,7 +394,7 @@ static void lcdif_crtc_mode_set_nofb(struct lcdif_drm_private *lcdif,
>>>        struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode;
>>>        u32 bus_flags = 0;
>>>
>>> -     if (lcdif->bridge && lcdif->bridge->timings)
>>> +     if (lcdif->bridge->timings)
>>>                bus_flags = lcdif->bridge->timings->input_bus_flags;
>>>        else if (bridge_state)
>>>                bus_flags = bridge_state->input_bus_cfg.flags;
>>> @@ -463,30 +463,21 @@ static void lcdif_crtc_atomic_enable(struct drm_crtc *crtc,
>>>        struct drm_display_mode *m = &lcdif->crtc.state->adjusted_mode;
>>>        struct drm_bridge_state *bridge_state = NULL;
>>>        struct drm_device *drm = lcdif->drm;
>>> -     u32 bus_format = 0;
>>> +     u32 bus_format;
>>>        dma_addr_t paddr;
>>>
>>> -     /* If there is a bridge attached to the LCDIF, use its bus format */
>>> -     if (lcdif->bridge) {
>>> -             bridge_state =
>>> -                     drm_atomic_get_new_bridge_state(state,
>>> -                                                     lcdif->bridge);
>>> -             if (!bridge_state)
>>> -                     bus_format = MEDIA_BUS_FMT_FIXED;
>>> -             else
>>> -                     bus_format = bridge_state->input_bus_cfg.format;
>>> -
>>> -             if (bus_format == MEDIA_BUS_FMT_FIXED) {
>>> -                     dev_warn_once(drm->dev,
>>> -                                   "Bridge does not provide bus format, assuming MEDIA_BUS_FMT_RGB888_1X24.\n"
>>> -                                   "Please fix bridge driver by handling atomic_get_input_bus_fmts.\n");
>>> -                     bus_format = MEDIA_BUS_FMT_RGB888_1X24;
>>> -             }
>>> -     }
>>> +     bridge_state = drm_atomic_get_new_bridge_state(state, lcdif->bridge);
>>> +     if (!bridge_state)
>>> +             bus_format = MEDIA_BUS_FMT_FIXED;
>>> +     else
>>> +             bus_format = bridge_state->input_bus_cfg.format;
>>
>> The code below seems to change the logic slightly.
>>
>> Could it happen that:
>> - bridge_state is valid (i.e. non-NULL)
>> - bridge_state->input_bus_cfg.format is set to 0 (i.e. not set) ?
>>     (note that MEDIA_BUS_FMT_FIXED is defined as 0x0001)
> 
> Yes, bridge_state->input_bus_cfg.format could be zero.
> Will keep the below default MEDIA_BUS_FMT_RGB888_1X24
> bus format setting in next version.

Thanks for confirming.

The rest of the series looks good, sorry for the delay in reviews.