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

From: Tim Harvey
Date: Tue Jul 18 2023 - 19:03:49 EST

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")

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.

best regards,

Tim