LKML Archive on
help / color / mirror / Atom feed
From: Geert Uytterhoeven <>
To: Bernardo Innocenti <>,
	Linux Frame Buffer Device Development 
Cc: lkml <>, aleph <>
Subject: Re: [Linux-fbdev-devel] How to mmap a shadow framebuffer in virtual memory
Date: Sun, 14 Jan 2007 12:13:20 +0100 (CET)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, 14 Jan 2007, Bernardo Innocenti wrote:
> This is driving me crazy.  I wrote this custom fb driver for an
> organic LED display for an embedded ARM system.
> The display is connected trough an I2C bus, therefore the display
> buffer is not memory mapped.
> Anyway, I want to support mmap() and my driver allocates shadow
> buffer with __get_free_pages() which gets periodically copied
> to the display by a thread. This is unlike most fb drivers which
> just point smem_start to the phisical address of their framebuffer.
> >From user space, opening /dev/fb0 and writing to it works just
> fine.  mmap()'ing the file and writing to it does not have any
> effect.
> Writing the phisical address in smem_start and letting the
> fbgen code do the rest didn't seem to work, so I reimplemented
> the fb_mmap hook.
> I don't feel confident with the Linux VM, so I tried several
> strategies to allocate the shadow buffer, including vmalloc()
> and kmalloc().
> The virtual framebuffer (vfb) also uses vmalloc() but crashes
> calling processes because it confuses physical and virtual
> addresses, or so it seems.
> Maybe it's just my kernel or my platform... does anybody use
> a similar technique?  Can anybody point me to known-good code
> that approximates my needs?

It's known to work for the PS3 frame buffer device driver, which copies the
virtual frame buffer to the GPU on every vsync. Check out ps3fb_mmap() in;a=blob_plain;f=drivers/video/ps3fb.c;hb=HEAD



Geert Uytterhoeven -- Sony Network and Software Technology Center Europe (NSCE) ------- The Corporate Village, Da Vincilaan 7-D1
Voice +32-2-7008453 Fax +32-2-7008622 ---------------- B-1935 Zaventem, Belgium

  reply	other threads:[~2007-01-14 11:13 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-14  0:24 Bernardo Innocenti
2007-01-14 11:13 ` Geert Uytterhoeven [this message]
2007-01-15  6:04   ` [Linux-fbdev-devel] " Bernardo Innocenti
2007-02-06 14:57     ` Bernardo Innocenti

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \
    --subject='Re: [Linux-fbdev-devel] How to mmap a shadow framebuffer in virtual memory' \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).