[PATCH v2 8/9] drm/simpledrm: Support virtual screen sizes

[Thomas Zimmermann]

Hi

Am 08.11.21 um 22:01 schrieb Noralf Trønnes:
> 
> 
> Den 01.11.2021 15.15, skrev Thomas Zimmermann:
>> Add constants for the maximum size of the shadow-plane surface
>> size. Useful for shadow planes with virtual screen sizes. The
>> current sizes are 4096 scanlines with 4096 pixels each. This
>> seems reasonable for current hardware, but can be increased as
>> necessary.
>>
>> In simpledrm, set the maximum framebuffer size from the constants
>> for shadow planes. Implements support for virtual screen sizes and
>> page flipping on the fbdev console.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> ---
>>   drivers/gpu/drm/tiny/simpledrm.c    |  9 +++++++--
>>   include/drm/drm_gem_atomic_helper.h | 18 ++++++++++++++++++
>>   2 files changed, 25 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
>> index e872121e9fb0..e42ae1c6ebcd 100644
>> --- a/drivers/gpu/drm/tiny/simpledrm.c
>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
>> @@ -2,6 +2,7 @@
>>   
>>   #include <linux/clk.h>
>>   #include <linux/of_clk.h>
>> +#include <linux/minmax.h>
>>   #include <linux/platform_data/simplefb.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/regulator/consumer.h>
>> @@ -776,6 +777,7 @@ static int simpledrm_device_init_modeset(struct simpledrm_device *sdev)
>>   	struct drm_display_mode *mode = &sdev->mode;
>>   	struct drm_connector *connector = &sdev->connector;
>>   	struct drm_simple_display_pipe *pipe = &sdev->pipe;
>> +	unsigned long max_width, max_height;
>>   	const uint32_t *formats;
>>   	size_t nformats;
>>   	int ret;
>> @@ -784,10 +786,13 @@ static int simpledrm_device_init_modeset(struct simpledrm_device *sdev)
>>   	if (ret)
>>   		return ret;
>>   
>> +	max_width = max_t(unsigned long, mode->hdisplay, DRM_SHADOW_PLANE_MAX_WIDTH);
>> +	max_height = max_t(unsigned long, mode->vdisplay, DRM_SHADOW_PLANE_MAX_HEIGHT);
>> +
>>   	dev->mode_config.min_width = mode->hdisplay;
>> -	dev->mode_config.max_width = mode->hdisplay;
>> +	dev->mode_config.max_width = max_width;
>>   	dev->mode_config.min_height = mode->vdisplay;
>> -	dev->mode_config.max_height = mode->vdisplay;
>> +	dev->mode_config.max_height = max_height;
>>   	dev->mode_config.prefer_shadow_fbdev = true;
>>   	dev->mode_config.preferred_depth = sdev->format->cpp[0] * 8;
>>   	dev->mode_config.funcs = &simpledrm_mode_config_funcs;
>> diff --git a/include/drm/drm_gem_atomic_helper.h b/include/drm/drm_gem_atomic_helper.h
>> index 48222a107873..54983ecf641a 100644
>> --- a/include/drm/drm_gem_atomic_helper.h
>> +++ b/include/drm/drm_gem_atomic_helper.h
>> @@ -22,6 +22,24 @@ int drm_gem_simple_display_pipe_prepare_fb(struct drm_simple_display_pipe *pipe,
>>    * Helpers for planes with shadow buffers
>>    */
>>   
>> +/**
>> + * DRM_SHADOW_PLANE_MAX_WIDTH - Maximum width of a plane's shadow buffer in pixels
>> + *
>> + * For drivers with shadow planes, the maximum width of the framebuffer is
>> + * usually independent from hardware limitations. Drivers can initialize struct
>> + * drm_mode_config.max_width from DRM_SHADOW_PLANE_MAX_WIDTH.
> 
> Why would a driver do that instead of using a value of its own? Is it
> some kind of standardization?

Exactly. The shadow framebuffer is in system memory, so its size is 
arbitrarily large. If each driver sets its own limit, it just fragments 
the DRM feature set. There's usually no reason why one driver can have 
4096 pixels and another one just 2048 or even 8192. Setting a constant 
harmonizes this among drivers.

Please note that nothing really depends on this value. Drivers can still 
use a different limit if they have to.

> 
>> + */
>> +#define DRM_SHADOW_PLANE_MAX_WIDTH	(1ul << 12)
> 
> Please use a decimal number, I'm so slow at doing this in my head that I
> use bash to calculate it for me, which really slows down parsing the code.

Ok. :D

Best regard
Thomas

> 
> Noralf.
> 
>> +
>> +/**
>> + * DRM_SHADOW_PLANE_MAX_HEIGHT - Maximum height of a plane's shadow buffer in scanlines
>> + *
>> + * For drivers with shadow planes, the maximum height of the framebuffer is
>> + * usually independent from hardware limitations. Drivers can initialize struct
>> + * drm_mode_config.max_height from DRM_SHADOW_PLANE_MAX_HEIGHT.
>> + */
>> +#define DRM_SHADOW_PLANE_MAX_HEIGHT	(1ul << 12)
>> +
>>   /**
>>    * struct drm_shadow_plane_state - plane state for planes with shadow buffers
>>    *
>>

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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