On Sat, 11 Nov 2006 11:03:51 +0100 Miguel Ojeda wrote:
> David, as akpm suggested, may this patch will solve the dcache aliasing problem?
>
> I will give you a introduction:
>
> The user mmaped page (got by __get_free_page()) is cfag12864b_buffer.
>
> The kernel only access it for reading at the same function 1 or 2 times:
>
> 1º memcmp() it against the cache, so we can tell if we must update the screen
> 2º if true, memcpy() the buffer to the cache buffer
>
> So, if we want the kernel to know the last state of the data, we should call
> flush_dcache_page() just once before we access it, right?
>
> The relevant code:
>
> flush_dcache_page(virt_to_page(cfag12864b_buffer));
> if (memcmp(cfag12864b_cache, cfag12864b_buffer, CFAG12864B_SIZE)) {
> memcpy(cfag12864b_cache, cfag12864b_buffer, CFAG12864B_SIZE);
>
> /***... update using cfag12864b_cache ...***/
> }
>
> You know, I can't test this stuff ;) so please review and check if it is right.
>
> Thanks you.
> ---
>
> - remove the "depends on x86" as it is portable again
>
> - memcpy() buffer to cache, then update from cache, not buffer,
> This way we only read the mmapped buffer 2 times.
>
> - add a flush_dcache_page() to flush the user mmaped page so
> the kernel has the last written data before accessing it.
>
> drivers/auxdisplay/Kconfig | 1 -
> drivers/auxdisplay/cfag12864b.c | 9 +++++----
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
> drivers-add-lcd-support-dcache.patch
> Signed-off-by: Miguel Ojeda Sandonis <[email protected]>
> ---
> diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
> index 8d41f72..ee30c48 100644
> --- a/drivers/auxdisplay/Kconfig
> +++ b/drivers/auxdisplay/Kconfig
> @@ -64,7 +64,6 @@ config KS0108_DELAY
>
> config CFAG12864B
> tristate "CFAG12864B LCD"
> - depends on X86
> depends on KS0108
> default n
> ---help---
Hi,
Shouldn't the framebuffer part of this code (cfag12864bfb) also
depend on CONFIG_FB? Without that, this build error occurs:
cfag12864bfb.c:(.init.text+0xc19d): undefined reference to `framebuffer_alloc'
cfag12864bfb.c:(.init.text+0xc211): undefined reference to `register_framebuffer'
cfag12864bfb.c:(.text+0xf2782): undefined reference to `unregister_framebuffer'
cfag12864bfb.c:(.text+0xf2789): undefined reference to `framebuffer_release'
(from 2.6.20-rc1-mm1)
so you may need to modify the Kconfig and Makefile to have a
separate config entry for cfag12864bfb (or is it always required?).
And while you are there (in the Kconfig file), please change
(hertzs) to (hertz).
---
~Randy
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