[PATCH v4 00/27] drm: Fix EDID reading on ti-sn65dsi86; solve some chicken-and-egg problems

[PATCH v4 00/27] drm: Fix EDID reading on ti-sn65dsi86; solve some chicken-and-egg problems

[Douglas Anderson]

The primary goal of this series is to try to properly fix EDID reading
for eDP panels using the ti-sn65dsi86 bridge.

Previously we had a patch that added EDID reading but it turned out
not to work at bootup. This caused some extra churn at bootup as we
tried (and failed) to read the EDID several times and also ended up
forcing us to use the hardcoded mode at boot. With this patch series I
believe EDID reading is reliable at boot now and we never use the
hardcoded mode.

This series is the logical successor to the 3-part series containing
the patch ("drm/bridge: ti-sn65dsi86: Properly get the EDID, but only
if refclk") [1] though only one actual patch is the same between the
two.

This series starts out with some general / obvious fixes and moves on
to some more specific and maybe controversial ones. I wouldn't object
to some of the earlier ones landing if they look ready.

This patch was developed agains linuxnext (next-20210416) on a
sc7180-trogdor-lazor device. To get things booting for me, I had to
use Stephen's patch [2] to keep from crashing but otherwise all the
patches I needed were here.

Primary change between v2 and v3 is to stop doing the EDID caching in
the core. I also added Andrzej's review tags.

Between v3 and v4 this series grew a whole lot. I changed it so that
the EDID reading is actually driven by the panel driver now as was
suggested by Andrzej. While I still believe that the old approach
wasn't too bad I'm still switching. Why?

The main reason is that I think it's useful in general for the panel
code to have access to the DDC bus and to be able to read the
EDID. This may allow us to more easily have the panel code support
multiple sources of panels--it can read the EDID and possibly adjust
timings based on the model ID. It also allows the panel code (or
perhaps backlight code?) to send DDC commands if they are need for a
particular panel.

At the moment, once the panel is provided the DDC bus then existing
code will assume that it should be in charge of reading the
EDID. While it doesn't have to work that way, it seems sane to build
on what's already there.

In order to expose the DDC bus to the panel, I had to solve a bunch of
chicken-and-egg problems in terms of probe ordering between the bridge
and the panel. I've broken the bridge driver into several sub drivers
to make this happen. At the moment the sub-drivers are just there to
solve the probe problem, but conceivably someone could use them to
break the driver up in the future if need be.

I apologize in advance for the length of this series. I'm currently
working through getting commit access to drm-misc [3] so I can land
the first several patches which are already reviewed. There are still
a lot of patches even after the first few, but hopefully you can see
that there are only so many because they're broken up into nice and
reviewable bite-sized-chunks. :-)

[1] https://lore.kernel.org/r/20210304155144.3.I60a7fb23ce4589006bc95c64ab8d15c74b876e68@changeid/
[2] https://lore.kernel.org/r/161706912161.3012082.17313817257247946143@swboyd.mtv.corp.google.com/
[3] https://gitlab.freedesktop.org/freedesktop/freedesktop/-/issues/348

Changes in v4:
- Reword commit mesage slightly.

Changes in v3:
- Removed "NOTES" from commit message.

Changes in v2:
- Removed 2nd paragraph in commit message.

Douglas Anderson (27):
  drm/bridge: Fix the stop condition of drm_bridge_chain_pre_enable()
  drm/bridge: ti-sn65dsi86: Simplify refclk handling
  drm/bridge: ti-sn65dsi86: Remove incorrectly tagged kerneldoc comment
  drm/bridge: ti-sn65dsi86: Reorder remove()
  drm/bridge: ti-sn65dsi86: Move drm_panel_unprepare() to post_disable()
  drm/bridge: ti-sn65dsi86: Get rid of the useless detect() function
  drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare /
    prepare
  drm/bridge: ti-sn65dsi86: Rename the main driver data structure
  drm/bridge: ti-sn65dsi86: More renames in prep for sub-devices
  drm/bridge: ti-sn65dsi86: Clean debugfs code
  drm/bridge: ti-sn65dsi86: Add local var for "dev" to simplify probe
  drm/bridge: ti-sn65dsi86: Cleanup managing of drvdata
  drm/bridge: ti-sn65dsi86: Use devm to do our runtime_disable
  drm/bridge: ti-sn65dsi86: Move all the chip-related init to the start
  drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into
    sub-drivers
  drm/panel: panel-simple: Get rid of hacky HPD chicken-and-egg code
  drm/bridge: ti-sn65dsi86: Use pm_runtime autosuspend
  drm/bridge: ti-sn65dsi86: Code motion of refclk management functions
  drm/bridge: ti-sn65dsi86: If refclk, DP AUX can happen w/out
    pre-enable
  drm/bridge: ti-sn65dsi86: Promote the AUX channel to its own sub-dev
  i2c: i2c-core-of: Fix corner case of finding adapter by node
  drm/panel: panel-simple: Remove extra call:
    drm_connector_update_edid_property()
  drm/panel: panel-simple: Power the panel when reading the EDID
  drm/panel: panel-simple: Cache the EDID as long as we retain power
  drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC
  arm64: dts: qcom: Link the panel to the bridge's DDC bus
  drm/panel: panel-simple: Prepare/unprepare are refcounted, not forced

 arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi |   1 +
 drivers/gpu/drm/bridge/Kconfig               |   1 +
 drivers/gpu/drm/bridge/ti-sn65dsi86.c        | 748 ++++++++++++-------
 drivers/gpu/drm/drm_bridge.c                 |   3 +
 drivers/gpu/drm/panel/Kconfig                |   1 +
 drivers/gpu/drm/panel/panel-simple.c         | 123 +--
 drivers/i2c/i2c-core-of.c                    |  17 +-
 7 files changed, 555 insertions(+), 339 deletions(-)

-- 
2.31.1.368.gbe11c130af-goog

[PATCH v4 21/27] i2c: i2c-core-of: Fix corner case of finding adapter by node

[Douglas Anderson]

The of_find_i2c_adapter_by_node() could end up failing to find an
adapter in certain conditions. Specifically it's possible that
of_dev_or_parent_node_match() could end up finding an I2C client in
the list and cause bus_find_device() to stop early even though an I2C
adapter was present later in the list.

Let's move the i2c_verify_adapter() into the predicate function to
prevent this. Now we'll properly skip over the I2C client and be able
to find the I2C adapter.

This issue has always been a potential problem if a single device tree
node could represent both an I2C client and an adapter. I believe this
is a sane thing to do if, for instance, an I2C-connected DP bridge
chip is present. The bridge chip is an I2C client but it can also
provide an I2C adapter (DDC tunneled over AUX channel). We don't want
to have to create a sub-node just so a panel can link to it with the
"ddc-i2c-bus" property.

I believe that this problem got worse, however, with commit
e814e688413a ("i2c: of: Try to find an I2C adapter matching the
parent"). Starting at that commit it would be even easier to
accidentally miss finding the adapter.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
This commit is sorta just jammed into the middle of my series. It has
no dependencies on the earlier patches in the series and I think it
can land independently in the i2c tree. Later patches in the series
won't work right without this one, but they won't crash. If we can't
find the i2c bus we'll just fall back to the hardcoded panel modes
which, at least today, all panels have.

I'll also note that part of me wonders if we should actually fix this
further to run two passes through everything: first look to see if we
find an exact match and only look at the parent pointer if there is no
match. I don't currently have a need for that and it's a slightly
bigger change, but it seems conceivable that it could affect someone?

(no changes since v1)

 drivers/i2c/i2c-core-of.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/i2c-core-of.c b/drivers/i2c/i2c-core-of.c
index 3ed74aa4b44b..de0bf5fce3a2 100644
--- a/drivers/i2c/i2c-core-of.c
+++ b/drivers/i2c/i2c-core-of.c
@@ -124,6 +124,14 @@ static int of_dev_or_parent_node_match(struct device *dev, const void *data)
 	return 0;
 }
 
+static int of_i2c_adapter_match(struct device *dev, const void *data)
+{
+	if (!of_dev_or_parent_node_match(dev, data))
+		return 0;
+
+	return !!i2c_verify_adapter(dev);
+}
+
 /* must call put_device() when done with returned i2c_client device */
 struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
 {
@@ -146,18 +154,13 @@ EXPORT_SYMBOL(of_find_i2c_device_by_node);
 struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
 {
 	struct device *dev;
-	struct i2c_adapter *adapter;
 
 	dev = bus_find_device(&i2c_bus_type, NULL, node,
-			      of_dev_or_parent_node_match);
+			      of_i2c_adapter_match);
 	if (!dev)
 		return NULL;
 
-	adapter = i2c_verify_adapter(dev);
-	if (!adapter)
-		put_device(dev);
-
-	return adapter;
+	return to_i2c_adapter(dev);
 }
 EXPORT_SYMBOL(of_find_i2c_adapter_by_node);
 
-- 
2.31.1.368.gbe11c130af-goog

Re: [PATCH v4 21/27] i2c: i2c-core-of: Fix corner case of finding adapter by node

[Bjorn Andersson]

On Fri 16 Apr 17:39 CDT 2021, Douglas Anderson wrote:

> The of_find_i2c_adapter_by_node() could end up failing to find an
> adapter in certain conditions. Specifically it's possible that
> of_dev_or_parent_node_match() could end up finding an I2C client in
> the list and cause bus_find_device() to stop early even though an I2C
> adapter was present later in the list.
> 
> Let's move the i2c_verify_adapter() into the predicate function to
> prevent this. Now we'll properly skip over the I2C client and be able
> to find the I2C adapter.
> 
> This issue has always been a potential problem if a single device tree
> node could represent both an I2C client and an adapter. I believe this
> is a sane thing to do if, for instance, an I2C-connected DP bridge
> chip is present. The bridge chip is an I2C client but it can also
> provide an I2C adapter (DDC tunneled over AUX channel). We don't want
> to have to create a sub-node just so a panel can link to it with the
> "ddc-i2c-bus" property.
> 
> I believe that this problem got worse, however, with commit
> e814e688413a ("i2c: of: Try to find an I2C adapter matching the
> parent"). Starting at that commit it would be even easier to
> accidentally miss finding the adapter.
> 

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> This commit is sorta just jammed into the middle of my series. It has
> no dependencies on the earlier patches in the series and I think it
> can land independently in the i2c tree. Later patches in the series
> won't work right without this one, but they won't crash. If we can't
> find the i2c bus we'll just fall back to the hardcoded panel modes
> which, at least today, all panels have.
> 

@Wolfram, I know it's late, but perhaps you could consider picking this
up for 5.13? It has no dependencies on the other patches in the series
and would simplify merging the rest in the next cycle.

Regards,
Bjorn

> I'll also note that part of me wonders if we should actually fix this
> further to run two passes through everything: first look to see if we
> find an exact match and only look at the parent pointer if there is no
> match. I don't currently have a need for that and it's a slightly
> bigger change, but it seems conceivable that it could affect someone?
> 
> (no changes since v1)
> 
>  drivers/i2c/i2c-core-of.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-of.c b/drivers/i2c/i2c-core-of.c
> index 3ed74aa4b44b..de0bf5fce3a2 100644
> --- a/drivers/i2c/i2c-core-of.c
> +++ b/drivers/i2c/i2c-core-of.c
> @@ -124,6 +124,14 @@ static int of_dev_or_parent_node_match(struct device *dev, const void *data)
>  	return 0;
>  }
>  
> +static int of_i2c_adapter_match(struct device *dev, const void *data)
> +{
> +	if (!of_dev_or_parent_node_match(dev, data))
> +		return 0;
> +
> +	return !!i2c_verify_adapter(dev);
> +}
> +
>  /* must call put_device() when done with returned i2c_client device */
>  struct i2c_client *of_find_i2c_device_by_node(struct device_node *node)
>  {
> @@ -146,18 +154,13 @@ EXPORT_SYMBOL(of_find_i2c_device_by_node);
>  struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
>  {
>  	struct device *dev;
> -	struct i2c_adapter *adapter;
>  
>  	dev = bus_find_device(&i2c_bus_type, NULL, node,
> -			      of_dev_or_parent_node_match);
> +			      of_i2c_adapter_match);
>  	if (!dev)
>  		return NULL;
>  
> -	adapter = i2c_verify_adapter(dev);
> -	if (!adapter)
> -		put_device(dev);
> -
> -	return adapter;
> +	return to_i2c_adapter(dev);
>  }
>  EXPORT_SYMBOL(of_find_i2c_adapter_by_node);
>  
> -- 
> 2.31.1.368.gbe11c130af-goog
> 

Re: [PATCH v4 00/27] drm: Fix EDID reading on ti-sn65dsi86; solve some chicken-and-egg problems

[Doug Anderson]

Hi,

On Fri, Apr 16, 2021 at 3:40 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> The primary goal of this series is to try to properly fix EDID reading
> for eDP panels using the ti-sn65dsi86 bridge.
>
> Previously we had a patch that added EDID reading but it turned out
> not to work at bootup. This caused some extra churn at bootup as we
> tried (and failed) to read the EDID several times and also ended up
> forcing us to use the hardcoded mode at boot. With this patch series I
> believe EDID reading is reliable at boot now and we never use the
> hardcoded mode.
>
> This series is the logical successor to the 3-part series containing
> the patch ("drm/bridge: ti-sn65dsi86: Properly get the EDID, but only
> if refclk") [1] though only one actual patch is the same between the
> two.
>
> This series starts out with some general / obvious fixes and moves on
> to some more specific and maybe controversial ones. I wouldn't object
> to some of the earlier ones landing if they look ready.
>
> This patch was developed agains linuxnext (next-20210416) on a
> sc7180-trogdor-lazor device. To get things booting for me, I had to
> use Stephen's patch [2] to keep from crashing but otherwise all the
> patches I needed were here.
>
> Primary change between v2 and v3 is to stop doing the EDID caching in
> the core. I also added Andrzej's review tags.
>
> Between v3 and v4 this series grew a whole lot. I changed it so that
> the EDID reading is actually driven by the panel driver now as was
> suggested by Andrzej. While I still believe that the old approach
> wasn't too bad I'm still switching. Why?
>
> The main reason is that I think it's useful in general for the panel
> code to have access to the DDC bus and to be able to read the
> EDID. This may allow us to more easily have the panel code support
> multiple sources of panels--it can read the EDID and possibly adjust
> timings based on the model ID. It also allows the panel code (or
> perhaps backlight code?) to send DDC commands if they are need for a
> particular panel.
>
> At the moment, once the panel is provided the DDC bus then existing
> code will assume that it should be in charge of reading the
> EDID. While it doesn't have to work that way, it seems sane to build
> on what's already there.
>
> In order to expose the DDC bus to the panel, I had to solve a bunch of
> chicken-and-egg problems in terms of probe ordering between the bridge
> and the panel. I've broken the bridge driver into several sub drivers
> to make this happen. At the moment the sub-drivers are just there to
> solve the probe problem, but conceivably someone could use them to
> break the driver up in the future if need be.
>
> I apologize in advance for the length of this series. I'm currently
> working through getting commit access to drm-misc [3] so I can land
> the first several patches which are already reviewed. There are still
> a lot of patches even after the first few, but hopefully you can see
> that there are only so many because they're broken up into nice and
> reviewable bite-sized-chunks. :-)
>
> [1] https://lore.kernel.org/r/20210304155144.3.I60a7fb23ce4589006bc95c64ab8d15c74b876e68@changeid/
> [2] https://lore.kernel.org/r/161706912161.3012082.17313817257247946143@swboyd.mtv.corp.google.com/
> [3] https://gitlab.freedesktop.org/freedesktop/freedesktop/-/issues/348
>
> Changes in v4:
> - Reword commit mesage slightly.
>
> Changes in v3:
> - Removed "NOTES" from commit message.
>
> Changes in v2:
> - Removed 2nd paragraph in commit message.
>
> Douglas Anderson (27):
>   drm/bridge: Fix the stop condition of drm_bridge_chain_pre_enable()
>   drm/bridge: ti-sn65dsi86: Simplify refclk handling
>   drm/bridge: ti-sn65dsi86: Remove incorrectly tagged kerneldoc comment
>   drm/bridge: ti-sn65dsi86: Reorder remove()
>   drm/bridge: ti-sn65dsi86: Move drm_panel_unprepare() to post_disable()
>   drm/bridge: ti-sn65dsi86: Get rid of the useless detect() function
>   drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare /
>     prepare

I have pushed the above 7 patches to drm-misc-next now so I don't have
to spam everyone with them for v5. The first patch is technically a
"fix" but I'm not aware of it affecting anyone in mainline and so I
didn't try to direct it to a fixes branch. The next 5 are trivial /
reviewed plenty. The last one is a bigger change but has Laurent's
review on it and it's been up on the lists for a while, so I sent it
in too.

I'll wait a few more days to see if any of the other "trivial" patches
early in the series get reviews and see if there is any other feedback
on the rest of the series. If I get reviews for some of the early
patches I'll likely try to push them before the v5.

-Doug