Hi Am 20.04.23 um 14:25 schrieb Geert Uytterhoeven:
Hi Thomas, On Thu, Apr 20, 2023 at 1:10 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:Am 20.04.23 um 12:04 schrieb Sui Jingfeng:What will happen if the 'screen_size' is not page_size aligned and mmap will mapping in the granularity of pages ?You need to map at page granularity. If screen_size is not page-size aligned, there's this trailing buffer that is accessible, but cannot be displayed. But userspace has no direct way of knowing that, so let's ignore that problem for now.Userspace can know, if fb_fix_screeninfo.smem_{start,len} match the actual offset and size.
Can you elaborate? How can userspace detect/compute the actually usable space?
From grep'ing fbdev drivers, smem_len appears to be a multiple of the pagesize. (?) screen_size is not exported and line_length in the fixed portion. Or can line_length change between modes? In that case it should be (yres_virtual * line_length), right?
Best regards Thomas
Gr{oetje,eeting}s,
Geert
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)
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