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    SubjectRe: [RFC][PATCH 0/4] lcd: platform-lcd: Add lcd panel and device tree support
    Hi Olof,

    On 2 January 2012 12:18, Olof Johansson <> wrote:
    > Hi,
    > On Sun, Jan 1, 2012 at 9:54 PM, Thomas Abraham
    > <> wrote:
    >> The platform-lcd driver depends on platform-specific callbacks to setup the
    >> lcd panel. These callbacks are supplied using driver's platform data. But
    >> for adding device tree support for platform-lcd driver, providing such
    >> callbacks is not possible (without using auxdata).
    >> Since the callbacks are usually lcd panel specific, it is possible to include
    >> the lcd panel specific setup and control functionality in the platform-lcd
    >> driver itself, thereby eliminating the need for supplying platform specific
    >> callbacks to the driver. The platform-lcd driver can include support for
    >> multiple lcd panels.
    >> This patchset removes the need for platform data for platform-lcd driver and
    >> adds support which can be used to implement lcd panel specific functionality
    >> in the driver. As an example, the support for Hydis hv070wsa lcd panel is added
    >> to the platform-lcd driver which is then used on the Exynos4 based Origen board.
    >> This currently breaks build for other users of platform-lcd driver. Those can be
    >> fixed if this approach is acceptable.
    > I think it would be a better idea to provide a generic binding for the
    > simple LCD panels that just need one or two power GPIOs to be turned
    > on (some tend to need one to activate and one for power control --
    > second might in some cases be handled through a regulator I suppose).
    > I'm sure there will be exceptions to this; panels that have quirks or
    > requirements on various things that will either require an expanded
    > binding, or custom probe functions.

    A majority of the existing users of the platform-lcd driver are using
    a single gpio to enable or disable the display. As you mentioned, a
    generic binding can be added for such lcd panels. There are other
    implementations that use one or more gpios but requires toggling those
    gpios in a panel specific way (usually with some delay). Such
    implementations will require custom panel support included in the
    platfrom-lcd driver. I will prepare a patch for these cases.

    > Especially in the case you are providing -- that lcd driver is only
    > using a single gpio, and it would be much more valuable to have a
    > trivial binding for this that uses shared code for this. Otherwise
    > every single simple panel will need to be added over time.

    Yes. I agree. It is better to have a common binding and there are many
    panels that can use this generic binding. I will make these changes.

    Thanks for your review.


    > -Olof

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