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

[Tim Harvey]

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.

best regards,

Tim