Den 12.03.2017 21.40, skrev Daniel Vetter:
On Sun, Mar 12, 2017 at 09:17:00PM +0100, Noralf Trønnes wrote:
Den 12.03.2017 20.16, skrev Daniel Vetter:
On Sun, Mar 12, 2017 at 06:50:17PM +0100, Daniel Vetter wrote:
Hi Noralf,
On Sat, Mar 11, 2017 at 10:35:31PM +0100, Noralf Trønnes wrote:
Add support for displays that have a register interface and can be
operated using a simple vtable.
I have looked through the staging/fbtft drivers and it seems that,
except the MIPI controllers, most if not all controllers are operated
through a register. And since most controllers have more than one bus
interface option, regmap seems like a good choice to describe the
interface (tested[1,2]).
MIPI DCS can't be represented using regmap since some commands doesn't
have a parameter. That would be like a register without a value, which
doesn't make sense.
In my second RFC of tinydrm I used drm_panel to decribe the panels
since it was a good match to the fbtft displays. I was then told that
drm_panel wasn't supposed to used like that, so I dropped it and have
tried to use the drm_simple_display_pipe_funcs vtable directly. This
hasn't been all successful, since I ended up using devm_add_action() to
power down the controller at the right time. Thierry Reding wasn't
happy with this and suggested "to add an explicit callback somewhere".
My solution has been to copy the drm_panel_funcs vtable.
Since I now have a vtable, I also added a callback to flush the
framebuffer. So presumably all the fbtft drivers can now be operated
through the tinydrm_panel_funcs vtable.
Ehrm, what? I admit I didn't follow the discussion in-depth, but if
drm_panel can't be used to describe a panel, it's not fit for the job and
needs to be extended. Adding even more abstraction, matroschka-style,
isn't a solution.
Personally I think tinydrm itself is already a bit much wrapping, but I
see that for really simple drivers it has it's uses. But more layers feels
like going in the wrong direction.
For the callback you're looking for (i.e. the regulator_disable call) I
think the correct place is to enable/disable the regulator in the
enable/disable hooks of the drm_simple_display_pipe functions. Or maybe in
their equivalent in drm_panel (well, probably pre_enable and post_disable,
since I guess you need that regulator to driver anything). Same for _init,
if the display is completely off there's no point in keeping the hw
running. Enabling/disabling the entire hw is pretty much what ->enable and
->disable are for. This also gives you proper runtime pm for almost for
free ...
Also, since the regulator is actually stored in struct mipi_dbi, it's
probably best to handle it in the mipi_dbi helpers too. You do that
already with the backlight anyway.
I noticed that the version of tinydrm that landed doesn't use drm_panel
anymore, I thought that was the case once, and for the version I acked?
Self-correct, there never was a version with drm_panel. tbh I think that's
perfectly fine, tinydrm is aimed at simple panels behind spi/i2c buses
(where also the entire video data is uploaded through spi/i2c, not just
control information). Not changing anything like I recommend seems like
the right action still (well, shuffling the regulator into
simple_pipe->enable/disable like I think it should be).
I have looked at the emails, and I used drm_panel in the first RFC,
but I got the impression that Thierry didn't like it so it was dropped
in RFC v2.
Hm, I thought I checked all the old versions of your example tinydrm
submissions and didn't find any with drm_panel. Do you have a link to
archives? I'd like to read Thierry's aguments, in case I'm oblivious to a
bad corner case :-)
I used drm_panel in the first tinydrm RFC in March 2016:
https://lists.freedesktop.org/archives/dri-devel/2016-March/102903.html
struct tinydrm_device {
struct drm_device *base;
struct drm_panel panel;
...
};
Then you commented:
https://lists.freedesktop.org/archives/dri-devel/2016-March/102921.html
> In the case of tinydrm I think that means we should have a bunch of new
> drm helpers, or extensions for existing ones:
<snip>
> - A helper to create a simple drm_connector from a drm_panel (the
> get_modes hooks you have here), maybe also in drm_simple_kms_helper.c.
So I made:
[PATCH 4/4] drm/panel: Add helper for simple panel connector
https://lists.freedesktop.org/archives/dri-devel/2016-May/106890.html
Thierry replied:
https://lists.freedesktop.org/archives/dri-devel/2016-May/107023.html
> Okay, that gives me a better understanding of where things are headed.
> That said, why would these devices even need to deal with drm_panel in
> the first place? Sounds to me like they are devices on some sort of
> control bus that you talk to directly. And they will represent
> essentially the panel with its built-in display controller.
>
> drm_panel on the other hand was designed as an interface between display
> controllers and panels, with the goal to let any display controller talk
> to any panel.
>
> While I'm sure you can support these types of simple panels using the
> drm_panel infrastructure I'm not sure it's necessary, since your driver
> will always talk to the panel directly, and hence the code to deal with
> the panel specifics could be part of the display pipe functions.
The reason for making this patchset was to solve a problem of power
management that Thierry pointed out in the mi0283qt driver where I use
devm_add_action() to disable the regulator on module/device unload.
I haven't found a way to do PM in the simple drm pipeline.
I use drm_simple_display_pipe.enable to enable backlight since it's
called after drm_simple_display_pipe.update. If it was called before,
then I could use it to prepare the panel/controller. I remember having
seen some comments in the atomic code about reordering something to
make it match PM better. But if .enable() could be called before
.update(), how then do I control backlight?
So what everyone else does is enable the backlight in ->enable (with the
screen just displaying black) and updating the screen contents in ->update
afterwards. That's what the comment in the docs about reordering stuff to
make it better fit with runtime PM.
If you don't like that for tinydrm, you can insert a call to ->update in
your ->enable. Slightly redundant, but then enabling a screen is not the
fastest thing so not much problem if you're inefficient. And you could
still fix that with a special case in ->update, but really not sure this
is worth it.
Once the screen is on you just get calls to ->update, so then it doesn't
matter anymore.
And with this ordering you should be able to stuff the regulator calls
into ->enable. On the disable side the same thing, but inverse ordering.
Thanks, I'll try that.
Noralf.
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