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SubjectRe: [PATCH] drm/atmel-hlcdc: add command line option to specify preferred depth
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On 2018-03-28 09:34, Boris Brezillon wrote:
> Hi Peter,
>
> On Mon, 26 Mar 2018 09:35:02 +0200
> Peter Rosin <peda@axentia.se> wrote:
>
>> I have an sama5d31-based system with 64MB of memory and a 1920x1080
>> LVDS display wired for 16-bpp. When I enable legacy fbdev support,
>> the contiguous memory allocator invariably fails with the order-11
>> allocation for a 1920x1080@24-bpp buffer (~6MB). But this HW can never
>> make any good use of RGB888, so that is a wasted attempt anyway that
>> would also waste precious memory should it succeed.
>>
>> Sure, I could rewrite user-space to go directly to KMS etc, and that
>> makes the (attempted) order-11 allocation go away, replacing it with
>> one order-10 allocation per application restart for a 1920x1080@16-bpp
>> buffer (<4MB). But after a few restarts, order-10 allocations start to
>> fail as well, which is only to be expected AFAIU.
>>
>> So, I'd rather not change user-space (which was originally written
>> to target a smaller display) so that I at the same time get the
>> benefit of an early pre-allocated fbdev frame-buffer that can be
>> reused over and over. But to do that I need to tell the driver that
>> 16-bpp is the preferred depth. Add a module parameter to do just that.
>>
>> Signed-off-by: Peter Rosin <peda@axentia.se>
>> ---
>> drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c | 18 +++++++++++++++++-
>> 1 file changed, 17 insertions(+), 1 deletion(-)
>>
>> I found some inspiration regarding naming and implementation here:
>> https://patchwork.kernel.org/patch/9848631/
>>
>> I have found no feedback on that patch though, which makes me wonder if
>> I'm perhaps barking up the wronig tree?
>
> Hm, isn't that something you can already overload with the video=
> parameter?
>
> video=<output>:<resolution>[-<bpp>]

Heh, you are right...

> AFAIR, <bpp> encodes the color depth, so what is the benefit of adding
> this new property to overload the default depth?

...but hhhmmm, I think I will have to have to encode the display size
in the bootargs so I will have to use distinct barebox environments
depending on the panel, but that's no biggie.

Splendid, please throw away the patch!

Cheers,
Peter

> Maybe I'm wrong and the default depth param is actually useful, but in
> this case we should probably make it generic since other drivers seems
> to need it too, and we might want to attach it to a specific display
> engine instance.
>
> Thanks,
>
> Boris
>
>>
>> Cheers,
>> Peter
>>
>> diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
>> index c1ea5c36b006..f0148627c221 100644
>> --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
>> +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
>> @@ -29,6 +29,11 @@
>>
>> #define ATMEL_HLCDC_LAYER_IRQS_OFFSET 8
>>
>> +static int atmel_hlcdc_preferred_depth __read_mostly;
>> +
>> +MODULE_PARM_DESC(preferreddepth, "Set preferred bpp");
>> +module_param_named(preferreddepth, atmel_hlcdc_preferred_depth, int, 0400);
>> +
>> static const struct atmel_hlcdc_layer_desc atmel_hlcdc_at91sam9n12_layers[] = {
>> {
>> .name = "base",
>> @@ -590,6 +595,7 @@ static int atmel_hlcdc_dc_modeset_init(struct drm_device *dev)
>> dev->mode_config.min_height = dc->desc->min_height;
>> dev->mode_config.max_width = dc->desc->max_width;
>> dev->mode_config.max_height = dc->desc->max_height;
>> + dev->mode_config.preferred_depth = 24;
>> dev->mode_config.funcs = &mode_config_funcs;
>>
>> return 0;
>> @@ -658,7 +664,7 @@ static int atmel_hlcdc_dc_load(struct drm_device *dev)
>>
>> platform_set_drvdata(pdev, dev);
>>
>> - drm_fb_cma_fbdev_init(dev, 24, 0);
>> + drm_fb_cma_fbdev_init(dev, atmel_hlcdc_preferred_depth, 0);
>>
>> drm_kms_helper_poll_init(dev);
>>
>> @@ -756,6 +762,16 @@ static int atmel_hlcdc_dc_drm_probe(struct platform_device *pdev)
>> struct drm_device *ddev;
>> int ret;
>>
>> + switch (atmel_hlcdc_preferred_depth) {
>> + case 0: /* driver default */
>> + case 8:
>> + case 16:
>> + case 24:
>> + break;
>> + default:
>> + return -EINVAL;
>> + }
>> +
>> ddev = drm_dev_alloc(&atmel_hlcdc_dc_driver, &pdev->dev);
>> if (IS_ERR(ddev))
>> return PTR_ERR(ddev);
>
>
>

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