Re: [PATCH v2 1/2] drm: bridge: samsung-dsim: Fix i.MX8M enable flow to meet spec

[Frieder Schrempf]

On 19.07.23 18:34, Tim Harvey wrote:
> On Wed, Jul 19, 2023 at 12:05 AM Frieder Schrempf
> <frieder.schrempf@xxxxxxxxxx> wrote:
>>
>> Hi Tim,
>>
>> On 19.07.23 01:03, Tim Harvey wrote:
>>> On Thu, Jul 13, 2023 at 3:01 AM Frieder Schrempf
>>> <frieder.schrempf@xxxxxxxxxx> wrote:
>>>>
>>>> Hi Tim,
>>>>
>>>> On 13.07.23 09:18, Frieder Schrempf wrote:
>>>>> Hi Tim,
>>>>>
>>>>> On 13.07.23 00:34, Tim Harvey wrote:
>>>>>> On Wed, May 3, 2023 at 9:33 AM Frieder Schrempf <frieder@xxxxxxx> wrote:
>>>>>>>
>>>>>>> From: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
>>>>>>>
>>>>>>> According to the documentation [1] the proper enable flow is:
>>>>>>>
>>>>>>> 1. Enable DSI link and keep data lanes in LP-11 (stop state)
>>>>>>> 2. Disable stop state to bring data lanes into HS mode
>>>>>>>
>>>>>>> Currently we do this all at once within enable(), which doesn't
>>>>>>> allow to meet the requirements of some downstream bridges.
>>>>>>>
>>>>>>> To fix this we now enable the DSI in pre_enable() and force it
>>>>>>> into stop state using the FORCE_STOP_STATE bit in the ESCMODE
>>>>>>> register until enable() is called where we reset the bit.
>>>>>>>
>>>>>>> We currently do this only for i.MX8M as Exynos uses a different
>>>>>>> init flow where samsung_dsim_init() is called from
>>>>>>> samsung_dsim_host_transfer().
>>>>>>>
>>>>>>> [1] https://docs.kernel.org/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation
>>>>>>>
>>>>>>> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
>>>>>>> ---
>>>>>>> Changes for v2:
>>>>>>> * Drop RFC
>>>>>>> ---
>>>>>>>  drivers/gpu/drm/bridge/samsung-dsim.c | 25 +++++++++++++++++++++++--
>>>>>>>  1 file changed, 23 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
>>>>>>> index e0a402a85787..9775779721d9 100644
>>>>>>> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
>>>>>>> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
>>>>>>> @@ -859,6 +859,10 @@ static int samsung_dsim_init_link(struct samsung_dsim *dsi)
>>>>>>>         reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
>>>>>>>         reg &= ~DSIM_STOP_STATE_CNT_MASK;
>>>>>>>         reg |= DSIM_STOP_STATE_CNT(driver_data->reg_values[STOP_STATE_CNT]);
>>>>>>> +
>>>>>>> +       if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type))
>>>>>>> +               reg |= DSIM_FORCE_STOP_STATE;
>>>>>>> +
>>>>>>>         samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
>>>>>>>
>>>>>>>         reg = DSIM_BTA_TIMEOUT(0xff) | DSIM_LPDR_TIMEOUT(0xffff);
>>>>>>> @@ -1340,6 +1344,9 @@ static void samsung_dsim_atomic_pre_enable(struct drm_bridge *bridge,
>>>>>>>                 ret = samsung_dsim_init(dsi);
>>>>>>>                 if (ret)
>>>>>>>                         return;
>>>>>>> +
>>>>>>> +               samsung_dsim_set_display_mode(dsi);
>>>>>>> +               samsung_dsim_set_display_enable(dsi, true);
>>>>>>>         }
>>>>>>>  }
>>>>>>>
>>>>>>> @@ -1347,9 +1354,16 @@ static void samsung_dsim_atomic_enable(struct drm_bridge *bridge,
>>>>>>>                                        struct drm_bridge_state *old_bridge_state)
>>>>>>>  {
>>>>>>>         struct samsung_dsim *dsi = bridge_to_dsi(bridge);
>>>>>>> +       u32 reg;
>>>>>>>
>>>>>>> -       samsung_dsim_set_display_mode(dsi);
>>>>>>> -       samsung_dsim_set_display_enable(dsi, true);
>>>>>>> +       if (samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type)) {
>>>>>>> +               samsung_dsim_set_display_mode(dsi);
>>>>>>> +               samsung_dsim_set_display_enable(dsi, true);
>>>>>>> +       } else {
>>>>>>> +               reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
>>>>>>> +               reg &= ~DSIM_FORCE_STOP_STATE;
>>>>>>> +               samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
>>>>>>> +       }
>>>>>>>
>>>>>>>         dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
>>>>>>>  }
>>>>>>> @@ -1358,10 +1372,17 @@ static void samsung_dsim_atomic_disable(struct drm_bridge *bridge,
>>>>>>>                                         struct drm_bridge_state *old_bridge_state)
>>>>>>>  {
>>>>>>>         struct samsung_dsim *dsi = bridge_to_dsi(bridge);
>>>>>>> +       u32 reg;
>>>>>>>
>>>>>>>         if (!(dsi->state & DSIM_STATE_ENABLED))
>>>>>>>                 return;
>>>>>>>
>>>>>>> +       if (!samsung_dsim_hw_is_exynos(dsi->plat_data->hw_type)) {
>>>>>>> +               reg = samsung_dsim_read(dsi, DSIM_ESCMODE_REG);
>>>>>>> +               reg |= DSIM_FORCE_STOP_STATE;
>>>>>>> +               samsung_dsim_write(dsi, DSIM_ESCMODE_REG, reg);
>>>>>>> +       }
>>>>>>> +
>>>>>>>         dsi->state &= ~DSIM_STATE_VIDOUT_AVAILABLE;
>>>>>>>  }
>>>>>>>
>>>>>>> --
>>>>>>> 2.40.0
>>>>>>>
>>>>>>
>>>>>> Hi Frieder,
>>>>>>
>>>>>> I found this patch to break mipi-dsi display on my board which has:
>>>>>>  - FocalTech FT5406 10pt touch controller (with no interrupt)
>>>>>>  - Powertip PH800480T013-IDF02 compatible panel
>>>>>>  - Toshiba TC358762 compatible DSI to DBI bridge
>>>>>>  - ATTINY based regulator used for backlight controller and panel enable
>>>>>>
>>>>>> I enable this via a dt overlay in a pending patch
>>>>>> imx8mm-venice-gw72xx-0x-rpidsi.dtso [1] which works on 6.4 but not
>>>>>> 6.5-rc1 which has this patch.
>>>>>>
>>>>>> The issue appears as:
>>>>>> [    6.110585] samsung-dsim 32e60000.dsi: xfer timed out: 29 06 00 00
>>>>>> 64 01 05 00 00 00
>>>>>> [    6.326588] tc358762 32e60000.dsi.0: error initializing bridge (-110)
>>>>>>
>>>>>> Instead of
>>>>>> [    1.011729] samsung-dsim 32e10000.dsi: supply vddcore not found,
>>>>>> using dummy regulator
>>>>>> [    1.019829] samsung-dsim 32e10000.dsi: supply vddio not found,
>>>>>> using dummy regulator
>>>>>> [    5.649928] samsung-dsim 32e10000.dsi:
>>>>>> [drm:samsung_dsim_host_attach] Attached tc358762 device
>>>>>>
>>>>>> I'm curious what board/panel were you needing this for and do you have
>>>>>> any ideas why it broke my setup?
>>>>>>
>>>>>> I'm also curious what board/panel Alexander tested this with and if
>>>>>> Adam or Jagan (or others) have tested this with their hardware?
>>>>>
>>>>> Sorry for breaking your setup. My test- and use-case is the same as
>>>>> Alexander's. I have the SN65DSI84 downstream bridge and without this
>>>>> patch it fails to come up in some cases.
>>>>>
>>>>> The failure is probably related to your downstream bridge being
>>>>> controlled by the DSI itself using command mode. The SN65DSI84 is
>>>>> instead controlled via I2C.
>>>>>
>>>>> Actually we should have tested this with a bridge that uses command mode
>>>>> before merging, now that I think of it. But I wasn't really aware of
>>>>> this until now.
>>>>>
>>>>> I'll have a closer look at the issue and then will get back to you. In
>>>>> the meantime if anyone can help analyze the problem or has proposals how
>>>>> to fix it, please let us know.
>>>>
>>>> With my patch samsung_dsim_init() now initializes the DSIM to stop
>>>> state. When being called from samsung_dsim_atomic_pre_enable() this
>>>> works as the stop state is cleared later in samsung_dsim_atomic_enable().
>>>>
>>>> When being called from samsung_dsim_host_transfer() to handle transfers
>>>> before samsung_dsim_atomic_pre_enable() was called, the stop state is
>>>> never cleared and transfers will fail.
>>>>
>>>> This is the case in your setup as tc358762_init() is called in
>>>> tc358762_pre_enable().
>>>>
>>>> I think that requiring to initialize the DSI host during transfer could
>>>> be avoided in this case by moving tc358762_init() from
>>>> tc358762_pre_enable() to tc358762_enable().
>>>>
>>>> But at the same time according to the docs at [1] this seems to be a
>>>> valid case that we need to support in the DSIM driver:
>>>>
>>>>   Whilst it is valid to call host_transfer prior to pre_enable or
>>>>   after post_disable, the exact state of the lanes is undefined at
>>>>   this point. The DSI host should initialise the interface, transmit
>>>>   the data, and then disable the interface again.
>>>>
>>>> Therefore I would propose to try a fix like in the attachement. If you
>>>> could test this, that would be great.
>>>>
>>>> Thanks
>>>> Frieder
>>>>
>>>> [1]
>>>> https://docs.kernel.org/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation
>>>
>>> Hi Frieder,
>>>
>>> The patch does not resolve the issue. I still get the 'xfer timed out'
>>> from samsung-dsim but noticing today that this issue doesn't exist in
>>> linux-next I've found that its resolved by Marek's patch:
>>> commit 8a4b2fc9c91a ("drm/bridge: tc358762: Split register programming
>>> from pre-enable to enable")
>>
>> Thanks for testing. I didn't notice there already is a patch from Marek
>> for the tc358762 driver. This is exactly the change that I was
>> considering above as a fix on the downstream bridge side.
>>
>>>
>>> I'm not clear on how that patch is staged in linux-next. If we can get
>>> that pulled into 6.5 then it will resolve the breakage.
>>
>> Still the documentation says that the DSI host must be able to handle
>> this and there might be other drivers that are not yet fixed like this
>> or can't be changed to make DSI transfers only after the host's
>> pre_enable() was called.
>>
>> Therefore I would prefer to fix the DSIM driver and apply this fix to
>> 6.5-rc instead of backporting the tc358762 patch. I gave it another shot
>> and maybe you could do one more test with the attached patch and without
>> the fix in tc358762.
>>
> 
> Frieder,
> 
> This patch doesn't resolve the issue either. Let me know if there is
> some quick debugging you want to add somewhere. I don't have a lot of
> time to troubleshoot this week as I'm trying to wrap up some work
> before a 2-week vacation but it's quick for me to apply patches and do
> a quick boot test.

Ok, thanks for testing anyway. I think I need to go back to the drawing
board with this as I'm obviously missing something. I won't bother you
more before I did some more research myself.