[PATCH v4 04/11] drm/bridge: Make the bridge chain a double-linked list

[Marek Szyprowski]

Hi Boris,

On 16.12.2019 16:25, Boris Brezillon wrote:
> On Mon, 16 Dec 2019 16:02:36 +0100
> Marek Szyprowski <m.szyprowski at samsung.com> wrote:
>> Hi Boris,
>>
>> On 16.12.2019 15:55, Boris Brezillon wrote:
>>> On Mon, 16 Dec 2019 14:54:25 +0100
>>> Marek Szyprowski <m.szyprowski at samsung.com> wrote:
>>>> On 03.12.2019 15:15, Boris Brezillon wrote:
>>>>> So that each element in the chain can easily access its predecessor.
>>>>> This will be needed to support bus format negotiation between elements
>>>>> of the bridge chain.
>>>>>
>>>>> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
>>>>> Reviewed-by: Neil Armstrong <narmstrong at baylibre.com>
>>>>> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>>>> I've noticed that this patch got merged to linux-next as commit
>>>> 05193dc38197021894b17239fafbd2eb1afe5a45. Sadly it breaks booting of
>>>> Samsung Exynos5250-based Arndale board. Booting stops after following
>>>> messages:
>>>>
>>>> [drm] Exynos DRM: using 14400000.fimd device for DMA mapping operations
>>>> exynos-drm exynos-drm: bound 14400000.fimd (ops fimd_component_ops)
>>>> exynos-drm exynos-drm: bound 14450000.mixer (ops mixer_component_ops)
>>>> exynos-drm exynos-drm: bound 14500000.dsi (ops exynos_dsi_component_ops)
>>>> exynos-drm exynos-drm: bound 14530000.hdmi (ops hdmi_component_ops)
>>>> [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
>>>> [drm] No driver support for vblank timestamp query.
>>>> [drm] Cannot find any crtc or sizes
>>>> [drm] Cannot find any crtc or sizes
>>>> [drm] Initialized exynos 1.1.0 20180330 for exynos-drm on minor 0
>>>>
>>>> I will try to debug this and provide more information soon.
>>>>   
>>> Can you try with this diff applied?
>> This patch doesn't change anything.
> Okay. Can you do a list_for_each_entry() on both encoder->bridge_chain
> and dsi->bridge_chain (dump bridge pointers in a pr_info()) before and
> after the list_splice_init() call?

encoder->bridge_chain contains only one element. dsi->drive_chain is empty.

Replacing that list_splice() with INIT_LIST_HEAD(&encoder->bridge_chain) 
fixed the boot issue. It looks that this is related with the way the 
Exynos DSI handles bridges (in bridge and out brige?). Maybe Andrzej 
will give a bit more detailed comment and spread some light on this.

I can send a formal patch fixing this if You want.

>>> --->8---
>>> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> index 3955f84dc893..118ecedc7621 100644
>>> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
>>> @@ -1523,7 +1523,7 @@ static int exynos_dsi_host_attach(struct mipi_dsi_host *host,
>>>           if (out_bridge) {
>>>                   drm_bridge_attach(encoder, out_bridge, NULL);
>>>                   dsi->out_bridge = out_bridge;
>>> -               list_splice(&encoder->bridge_chain, &dsi->bridge_chain);
>>> +               list_splice_init(&encoder->bridge_chain, &dsi->bridge_chain);
>>>           } else {
>>>                   int ret = exynos_dsi_create_connector(encoder);
>>>    
>>> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
>>> index 6c5b80ad6154..e1378d48210f 100644
>>> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
>>> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
>>> @@ -1613,7 +1613,7 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
>>>            * from our driver, since we need to sequence them within the
>>>            * encoder's enable/disable paths.
>>>            */
>>> -       list_splice(&dsi->encoder->bridge_chain, &dsi->bridge_chain);
>>> +       list_splice_init(&dsi->encoder->bridge_chain, &dsi->bridge_chain);
>>>    
>>>           if (dsi->port == 0)
>>>                   vc4_debugfs_add_regset32(drm, "dsi0_regs", &dsi->regset);
>>> @@ -1639,7 +1639,7 @@ static void vc4_dsi_unbind(struct device *dev, struct device *master,
>>>            * Restore the bridge_chain so the bridge detach procedure can happen
>>>            * normally.
>>>            */
>>> -       list_splice(&dsi->bridge_chain, &dsi->encoder->bridge_chain);
>>> +       list_splice_init(&dsi->bridge_chain, &dsi->encoder->bridge_chain);
>>>           vc4_dsi_encoder_destroy(dsi->encoder);
>>>    
>>>           if (dsi->port == 1)
>>>
>>>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland