Re: [PATCH v3 1/2] video: ARM CLCD: Add DT support

On Mon, Sep 23, 2013 at 10:30:15AM -0600, Stephen Warren wrote:

On 09/23/2013 10:06 AM, Russell King - ARM Linux wrote:

quoted

On Mon, Sep 23, 2013 at 10:03:18AM -0600, Stephen Warren wrote:

quoted

It sounds like you could just put LCDControl & 0x2e in the DT rather
than using values such as 0x100..0x107, which don't appear to match the
register format you mentioned above.

No.  Platforms which route the outputs to something like VGA or HDMI can
change the framebuffer format.  Your suggestions is far too restrictive.

Surely the DT should describe the HW setup only. Usually, a particular
HW setup can support multiple different framebuffer formats. Hence, the
DT wouldn't/shouldn't imply anything about the framebuffer format, but
simply which wires are connected to the LCD.

Quite, and putting the contents of the LCDControl register - even just
bits 5 and 3-1 results in you having to modify the DT and reboot the
kernel just to change the framebuffer format.  That's why I'm objecting
to your comment.

When I rewrote the way the CLCD driver handles the various panels, I did
it with full information on how the hardware was being used at that time.
That is precisely why I came up with the capability system, where we
describe which formats the hardware can support up to the interface,
separately from the formats which the attached device - be it a LCD
panel, VGA socket or HDMI socket - can support.  The resulting set of
formats which can be used are a union of these.

Suggesting that we can do this by putting register values into DT is
completely wrong - if that were possible, I wouldn't have come up with
this capability system to sort this mess out in the first place - I
could've just hard-coded the register values and said to everyone
"tough, on these platforms you only get RGB444 support and that's it."