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SubjectRe: [PATCH v2] video: simplefb: add mode parsing function
From
Hi

On Mon, May 27, 2013 at 5:53 AM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> The naming scheme of simplefb's mode is precise enough to allow building
> the mode structure from it instead of using a static list of modes. This
> patch introduces a function that does this. In case exotic modes that
> cannot be represented from their name alone are needed, the static list
> of modes is still available as a backup.
>
> It also changes the order in which colors are declared from MSB first to
> the more standard LSB first.
>
> Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
> ---
> Changes from v1:
> - amended documentation following Stephen's suggestion
> - allow parsing of bitfields larger than 9 bits
> - made it clear that the parsing order of bits is changed with respect
> to the original patch
>
> Andrew, since this patch introduces a (small) change in the DT bindings,
> could we try to merge it during the -rc cycle so we don't have to come
> with a more complex solution in the future?
>
> .../bindings/video/simple-framebuffer.txt | 12 +++-
> drivers/video/simplefb.c | 72 +++++++++++++++++++++-
> 2 files changed, 80 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/video/simple-framebuffer.txt b/Documentation/devicetree/bindings/video/simple-framebuffer.txt
> index 3ea4605..18d03e2 100644
> --- a/Documentation/devicetree/bindings/video/simple-framebuffer.txt
> +++ b/Documentation/devicetree/bindings/video/simple-framebuffer.txt
> @@ -10,8 +10,16 @@ Required properties:
> - width: The width of the framebuffer in pixels.
> - height: The height of the framebuffer in pixels.
> - stride: The number of bytes in each line of the framebuffer.
> -- format: The format of the framebuffer surface. Valid values are:
> - - r5g6b5 (16-bit pixels, d[15:11]=r, d[10:5]=g, d[4:0]=b).
> +- format: The format of the framebuffer surface. Described as a sequence of
> + channel/num-bits pairs, where each pair describes how many bits are used
> + by a given color channel. Value channels are "r" (red), "g" (green),
> + "b" (blue), "a" (alpha) and "x" (unused). Channels are listed in bit
> + order, starting from the LSB. For instance, a format named "r5g6b5"
> + describes a 16-bit format where red is encoded in the 5 less significant
> + bits, green in the 6 following ones, and blue in the 5 last:
> + BBBBBGGG GGGRRRRR
> + ^ ^
> + MSB LSB

Is there a specific reason why we need arbitrary RGB formats? I have a
KMS/DRM driver based on dvbe that can provide the exact same
functionality as this fbdev driver (including an fbdev
backwards-compat layer). However, DRM does not allow arbitrary formats
but rather provides a huge list of supported formats.

If we apply this patch it will get very hard to support this with a
KMS driver. So any reason why we cannot use the DRM FOURCC constants
instead?

The dvbe proposal is available here: (also see the two following patches)
http://lkml.indiana.edu/hypermail/linux/kernel/1302.2/00274.html

it provides a simple DRM driver that uses VESA / VBE. I am currently
trying to rework it to "SimpleDRM" which can support arbitrary
firmware framebuffers.

Cheers
David

> Example:
>
> diff --git a/drivers/video/simplefb.c b/drivers/video/simplefb.c
> index e2e9e3e..1430752 100644
> --- a/drivers/video/simplefb.c
> +++ b/drivers/video/simplefb.c
> @@ -21,6 +21,7 @@
> */
>
> #include <linux/errno.h>
> +#include <linux/ctype.h>
> #include <linux/fb.h>
> #include <linux/io.h>
> #include <linux/module.h>
> @@ -82,8 +83,72 @@ struct simplefb_format {
> struct fb_bitfield transp;
> };
>
> +static struct simplefb_format *simplefb_parse_format(struct device *dev,
> + const char *str)
> +{
> + struct simplefb_format *format;
> + unsigned int offset = 0;
> + unsigned int i = 0;
> +
> + format = devm_kzalloc(dev, sizeof(*format), GFP_KERNEL);
> + if (!format)
> + return ERR_PTR(-ENOMEM);
> +
> + while (str[i] != 0) {
> + struct fb_bitfield *field = NULL;
> + int length = 0;
> +
> + switch (str[i++]) {
> + case 'r':
> + case 'R':
> + field = &format->red;
> + break;
> + case 'g':
> + case 'G':
> + field = &format->green;
> + break;
> + case 'b':
> + case 'B':
> + field = &format->blue;
> + break;
> + case 'a':
> + case 'A':
> + field = &format->transp;
> + break;
> + case 'x':
> + case 'X':
> + break;
> + default:
> + goto error;
> + }
> +
> + if (!isdigit(str[i]))
> + goto error;
> +
> + while (isdigit(str[i])) {
> + length = length * 10 + (str[i++] - '0');
> + }
> +
> + if (field) {
> + field->offset = offset;
> + field->length = length;
> + }
> +
> + offset += length;
> + }
> +
> + format->bits_per_pixel = (offset + 7) & ~0x7;
> + format->name = str;
> + return format;
> +
> +error:
> + dev_err(dev, "Invalid format string\n");
> + return ERR_PTR(-EINVAL);
> +}
> +
> +/* if you use exotic modes that simplefb_parse_format cannot decode, you can
> + specify them here. */
> static struct simplefb_format simplefb_formats[] = {
> - { "r5g6b5", 16, {11, 5}, {5, 6}, {0, 5}, {0, 0} },
> };
>
> struct simplefb_params {
> @@ -131,7 +196,10 @@ static int simplefb_parse_dt(struct platform_device *pdev,
> params->format = &simplefb_formats[i];
> break;
> }
> - if (!params->format) {
> + if (!params->format)
> + params->format = simplefb_parse_format(&pdev->dev, format);
> +
> + if (IS_ERR(params->format)) {
> dev_err(&pdev->dev, "Invalid format value\n");
> return -EINVAL;
> }
> --
> 1.8.3
>
> --
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