Re: [PATCH] omapdrm: Make fixed resolution panels work

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On Monday 18 February 2013 02:01 PM, Tomi Valkeinen wrote:
On 2013-02-18 09:23, Archit Taneja wrote:

diff --git a/drivers/staging/omapdrm/omap_connector.c
b/drivers/staging/omapdrm/omap_connector.c
index 4cc9ee7..839c6e4 100644
--- a/drivers/staging/omapdrm/omap_connector.c
+++ b/drivers/staging/omapdrm/omap_connector.c
@@ -110,6 +110,11 @@ static enum drm_connector_status
omap_connector_detect(
                          ret = connector_status_connected;
                  else
                          ret = connector_status_disconnected;
+       } else if (dssdev->type == OMAP_DISPLAY_TYPE_DPI ||
+                       dssdev->type == OMAP_DISPLAY_TYPE_DBI ||
+                       dssdev->type == OMAP_DISPLAY_TYPE_SDI ||
+                       dssdev->type == OMAP_DISPLAY_TYPE_DSI) {
+               ret = connector_status_connected;

hmm, why not just have a default detect fxn for panel drivers which
always returns true?  Seems a bit cleaner.. otherwise, I guess we
could just change omap_connector so that if dssdev->detect is null,
assume always connected.  Seems maybe a slightly better way since
currently omap_connector doesn't really know too much about different
sorts of panels.  But I'm not too picky if that is a big pain because
we probably end up changing all this as CFP starts coming into
existence.

Same goes for check_timings/set_timings..  it seems a bit cleaner just
to have default fxns in the panel drivers that do-the-right-thing,
although I suppose it might be a bit more convenient for out-of-tree
panel drivers to just assume fixed panel if these fxns are null.

Yeah, I can't make my mind about null pointer. It's nice to inform with
a null pointer that the panel doesn't support the given operation, or
that it doesn't make sense, but handling the null value makes the code a
bit complex.

For example, our VENC driver doesn't know if there's a TV connected or
not, so neither true or false as connect return value makes sense there.
Or, for a DSI command mode panel, set_timings doesn't really make much
sense.

Maybe having default functions in omapdss might be a better idea. There
is an option of adding default functions in omap_dss_register_driver()
(drivers/video/omap2/dss/core.c).

Tomi, do you think it's fine to add some more default panel driver funcs?

We can add default funcs. However, adding them in
omap_dss_register_driver is not so nice, as it makes the omap_dss_driver
(which is essentially an "ops" struct) non-constable. Instead, we should
move the setting of the default funcs to the drivers.

If I'm not mistaken, we could manage that with a helper macro. Assigning
a value to the same field of a struct should be ok by the compiler, and
should cause only the last assignment to be taken into use. So:

static struct foo zab = {
	.bar = 123, /* ignored */
	.bar = 234, /* used */
};

And so we could have:

static struct omap_dss_driver my_panel_driver = {
	OMAPDSS_DEFAULT_PANEL_OPS, /* macro for default ops */

	.enable = my_panel_enable,
	/* ... */
};

This sounds nice, but if the panel driver ops are going to be changed again in CPF, then it might make sense to do this later, depending on how it CPF handles default ops in panel drivers.

Maybe we should leave this patch as-is, since we know it will be modified later.

Archit

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