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Date:   Thu, 13 Jul 2023 12:01:40 +0200
From:   Frieder Schrempf <frieder.schrempf@...tron.de>
To:     Tim Harvey <tharvey@...eworks.com>,
        Frieder Schrempf <frieder@...s.de>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Adam Ford <aford173@...il.com>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        dri-devel@...ts.freedesktop.org, Inki Dae <inki.dae@...sung.com>,
        linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>, Marek Vasut <marex@...x.de>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>
Subject: Re: [PATCH v2 1/2] drm: bridge: samsung-dsim: Fix i.MX8M enable flow
 to meet spec

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@...s.de> wrote:
>>>
>>> From: Frieder Schrempf <frieder.schrempf@...tron.de>
>>>
>>> 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@...tron.de>
>>> ---
>>> 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
View attachment "0001-drm-bridge-samsung-dsim-Fix-init-during-host-transfe.patch" of type "text/x-patch" (3217 bytes)

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