linux-kernel - Re: [RFC PATCH v1 0/5] Add pardata bus + tinydrm driver

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Date:   Thu, 2 Aug 2018 21:46:43 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Noralf Trønnes <noralf@...nnes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [RFC PATCH v1 0/5] Add pardata bus + tinydrm driver

Hi Sam,

On Thu, Aug 2, 2018 at 9:39 PM, Sam Ravnborg <sam@...nborg.org> wrote:
> This is an RFC - to get some responses on the overall design.
> The code builds but has not yet been tested on any HW.
> Before investing more time into this I would like some feedback
> if this is the right way forward or a different design should
> be pursued.
>
> The problem to solve is that I have a propriatary ARM based board
> with a display that is connected using a parallel bus.
> The display is capable of showing graphics
> so it is more advanced than what is found in auxdisplay/

Just a quick note: the original intention of auxdisplay/ was not only
text displays (actually, the first drivers there --cfag12864b/ks0108--
were graphic displays). They have a very low resolution (e.g. 128x64
for cfag12864b), though.

Cheers,
Miguel

> I know there are others using a display connected
> usign a parallel data bus, so this is not a unique problem
> for my board alone. But I do not expect many users as
> any modern design likely uses SPI or similar.
>
> The old (proprietary) approach was to implement a char driver
> and then let some 3rd party lib use the char driver to write to the
> display.
> The goal is to move to a more modern world where I expect
> to have a simple Qt based program running that can
> be used for a few simple things.
> (I do not expect any high performance and do not need it).
>
> Implementation:
>
> A pardata bus is implemented.
> It uses a platform_driver to hook into the DT.
> When probed the pardatabus driver creates pardata devices
> for all child nodes in the tree.
>
> Within tinydrm the pardata support is used to implement
> a driver for the display I have (Winstar wg160160).
> A library module is used to implement the more basic
> things allowing us to have a more simple driver,
> and thus making it simpler to add new drivers.
>
> The implmentation uses array support in gpiolib
> to try to have some performance on screen updates.
>
>
> TODO:
> - Test on HW
> - Add locking so there can be more than one user on the bus
> - Improve pardata.rst documentation
> - Add support for a sparkfun parallel data display
>   (To verify that the library is generic)
> - I may add a class if I see the need
> - Likewise I may add sysfs attributes if there is a need for it
>
> Any comments appreciated!
>
>         Sam
>
>
> Sam Ravnborg (5):
>       dt-bindings: add parallel data bus (pardata)
>       pardata: new bus for parallel data access
>       tinydrm: add support for parallel data displays
>       dt-bindings: add winstar,wg160160 display bindings
>       tinydrm: add winstar wg160160 driver
>
>
>  .../bindings/display/winstar,wg160160.txt          |  53 +++
>  .../bindings/pardata/parallel-data-bus.txt         |  60 +++
>  Documentation/driver-api/index.rst                 |   1 +
>  Documentation/driver-api/pardata.rst               |  60 +++
>  MAINTAINERS                                        |  14 +
>  drivers/Kconfig                                    |   2 +
>  drivers/Makefile                                   |   1 +
>  drivers/gpu/drm/tinydrm/Kconfig                    |  13 +
>  drivers/gpu/drm/tinydrm/Makefile                   |   2 +
>  drivers/gpu/drm/tinydrm/pardata-dbi.c              | 417 +++++++++++++++++++++
>  drivers/gpu/drm/tinydrm/wg160160.c                 | 298 +++++++++++++++
>  drivers/pardata/Kconfig                            |  17 +
>  drivers/pardata/Makefile                           |   5 +
>  drivers/pardata/pardata.c                          | 282 ++++++++++++++
>  include/drm/tinydrm/pardata-dbi.h                  | 257 +++++++++++++
>  include/linux/pardata.h                            | 138 +++++++
>  16 files changed, 1620 insertions(+)