linux-kernel - Re: [PATCH davem] drivers: add LCD support

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Message-Id: <20061218093855.01445a7c.randy.dunlap@oracle.com>
Date:	Mon, 18 Dec 2006 09:38:55 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Miguel Ojeda" <maxextreme@...il.com>
Cc:	davem@...emloft.net, akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH davem] drivers: add LCD support

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 <maxextreme@...il.com>
> ---
> 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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