[PATCH] atmel_lcdfb: Correct fifo size for some products

[PATCH] atmel_lcdfb: Correct fifo size for some products

[Nicolas Ferre]

Remove wrong fifo size definition for some AT91 products.

Due to a misunderstanding of some AT91 datasheets, a fifo size of 2048 (words)
has been introduced by mistake. In fact, all products (AT91/AT32) are sharing
the same fifo size of 512 words.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
---
Can we consider this fix for .30-final ?

 drivers/video/atmel_lcdfb.c |   10 ++--------
 1 files changed, 2 insertions(+), 8 deletions(-)

diff --git a/drivers/video/atmel_lcdfb.c b/drivers/video/atmel_lcdfb.c
index 9a577a8..2fb63f6 100644
--- a/drivers/video/atmel_lcdfb.c
+++ b/drivers/video/atmel_lcdfb.c
@@ -29,14 +29,8 @@
 
 /* configurable parameters */
 #define ATMEL_LCDC_CVAL_DEFAULT		0xc8
-#define ATMEL_LCDC_DMA_BURST_LEN	8
-
-#if defined(CONFIG_ARCH_AT91SAM9263) || defined(CONFIG_ARCH_AT91CAP9) || \
-	defined(CONFIG_ARCH_AT91SAM9RL)
-#define ATMEL_LCDC_FIFO_SIZE		2048
-#else
-#define ATMEL_LCDC_FIFO_SIZE		512
-#endif
+#define ATMEL_LCDC_DMA_BURST_LEN	8	/* words */
+#define ATMEL_LCDC_FIFO_SIZE		512	/* words */
 
 #if defined(CONFIG_ARCH_AT91)
 #define	ATMEL_LCDFB_FBINFO_DEFAULT	(FBINFO_DEFAULT \
-- 
1.5.3.7



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Re: [PATCH] atmel_lcdfb: Correct fifo size for some products

[Haavard Skinnemoen]

Nicolas Ferre wrote:
> Remove wrong fifo size definition for some AT91 products.
> 
> Due to a misunderstanding of some AT91 datasheets, a fifo size of 2048 (words)
> has been introduced by mistake. In fact, all products (AT91/AT32) are sharing
> the same fifo size of 512 words.
> 
> Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
> ---
> Can we consider this fix for .30-final ?

Fine by me as it doesn't affect AVR32 in any way.

Haavard

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Re: [PATCH] atmel_lcdfb: Correct fifo size for some products

[Andrew Morton]

On Fri, 15 May 2009 12:34:18 +0200 Nicolas Ferre <nicolas.ferre@atmel.com> wrote:

> Remove wrong fifo size definition for some AT91 products.
> 
> Due to a misunderstanding of some AT91 datasheets, a fifo size of 2048 (words)
> has been introduced by mistake. In fact, all products (AT91/AT32) are sharing
> the same fifo size of 512 words.
> 

Changelog fails to describe the impact of the bug, so people who are
working out which kernel versions it should be ported into don't know
what to do.

Furthermore, people who are hitting a bug in this driver in older
kernel versions will have difficulty working out whether this patch
might fix their bug.

> Can we consider this fix for .30-final ?

Sure, but for what reason?

What about 2.6.29.x, 2.6.28.x, earlier?

> --- a/drivers/video/atmel_lcdfb.c
> +++ b/drivers/video/atmel_lcdfb.c
> @@ -29,14 +29,8 @@
>  
>  /* configurable parameters */
>  #define ATMEL_LCDC_CVAL_DEFAULT		0xc8
> -#define ATMEL_LCDC_DMA_BURST_LEN	8
> -
> -#if defined(CONFIG_ARCH_AT91SAM9263) || defined(CONFIG_ARCH_AT91CAP9) || \
> -	defined(CONFIG_ARCH_AT91SAM9RL)
> -#define ATMEL_LCDC_FIFO_SIZE		2048
> -#else
> -#define ATMEL_LCDC_FIFO_SIZE		512
> -#endif
> +#define ATMEL_LCDC_DMA_BURST_LEN	8	/* words */
> +#define ATMEL_LCDC_FIFO_SIZE		512	/* words */
>  
>  #if defined(CONFIG_ARCH_AT91)
>  #define	ATMEL_LCDFB_FBINFO_DEFAULT	(FBINFO_DEFAULT \


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Re: [PATCH] atmel_lcdfb: Correct fifo size for some products

[Nicolas Ferre]

Andrew Morton :
> On Fri, 15 May 2009 12:34:18 +0200 Nicolas Ferre <nicolas.ferre@atmel.com> wrote:
> 
>> Remove wrong fifo size definition for some AT91 products.
>>
>> Due to a misunderstanding of some AT91 datasheets, a fifo size of 2048 (words)
>> has been introduced by mistake. In fact, all products (AT91/AT32) are sharing
>> the same fifo size of 512 words.
>>
> 
> Changelog fails to describe the impact of the bug, so people who are
> working out which kernel versions it should be ported into don't know
> what to do.
> 
> Furthermore, people who are hitting a bug in this driver in older
> kernel versions will have difficulty working out whether this patch
> might fix their bug.

Ok, you are right, I will try to add some information.

In fact, if you mis-configure the fifo watermark making it too high you
end without the capacity of issuing burst transfers on the internal AHB
bus. This will decrease overall system performance as the LCD will ask
for data as soon as the fifo will have one byte available (not efficient
single accesses).

>> Can we consider this fix for .30-final ?
> 
> Sure, but for what reason?
> 
> What about 2.6.29.x, 2.6.28.x, earlier?

Indeed, should be valuable to extend this correction to stable kernel
series. I added Greg to the loop for this purpose.

>> --- a/drivers/video/atmel_lcdfb.c
>> +++ b/drivers/video/atmel_lcdfb.c
>> @@ -29,14 +29,8 @@
>>  
>>  /* configurable parameters */
>>  #define ATMEL_LCDC_CVAL_DEFAULT		0xc8
>> -#define ATMEL_LCDC_DMA_BURST_LEN	8
>> -
>> -#if defined(CONFIG_ARCH_AT91SAM9263) || defined(CONFIG_ARCH_AT91CAP9) || \
>> -	defined(CONFIG_ARCH_AT91SAM9RL)
>> -#define ATMEL_LCDC_FIFO_SIZE		2048
>> -#else
>> -#define ATMEL_LCDC_FIFO_SIZE		512
>> -#endif
>> +#define ATMEL_LCDC_DMA_BURST_LEN	8	/* words */
>> +#define ATMEL_LCDC_FIFO_SIZE		512	/* words */
>>  
>>  #if defined(CONFIG_ARCH_AT91)
>>  #define	ATMEL_LCDFB_FBINFO_DEFAULT	(FBINFO_DEFAULT \

Thanks to have taken immediately this patch into account ; even before
my late explanation ;-)

Best regards,
-- 
Nicolas Ferre


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Re: [PATCH] atmel_lcdfb: Correct fifo size for some products

[Greg KH]

On Mon, Jun 08, 2009 at 05:36:20PM +0200, Nicolas Ferre wrote:
> Andrew Morton :
> > On Fri, 15 May 2009 12:34:18 +0200 Nicolas Ferre <nicolas.ferre@atmel.com> wrote:
> > 
> >> Remove wrong fifo size definition for some AT91 products.
> >>
> >> Due to a misunderstanding of some AT91 datasheets, a fifo size of 2048 (words)
> >> has been introduced by mistake. In fact, all products (AT91/AT32) are sharing
> >> the same fifo size of 512 words.
> >>
> > 
> > Changelog fails to describe the impact of the bug, so people who are
> > working out which kernel versions it should be ported into don't know
> > what to do.
> > 
> > Furthermore, people who are hitting a bug in this driver in older
> > kernel versions will have difficulty working out whether this patch
> > might fix their bug.
> 
> Ok, you are right, I will try to add some information.
> 
> In fact, if you mis-configure the fifo watermark making it too high you
> end without the capacity of issuing burst transfers on the internal AHB
> bus. This will decrease overall system performance as the LCD will ask
> for data as soon as the fifo will have one byte available (not efficient
> single accesses).
> 
> >> Can we consider this fix for .30-final ?
> > 
> > Sure, but for what reason?
> > 
> > What about 2.6.29.x, 2.6.28.x, earlier?
> 
> Indeed, should be valuable to extend this correction to stable kernel
> series. I added Greg to the loop for this purpose.

For stable stuff, please send any requested patches, with the git commit
id of the patch in Linus's tree, to stable@kernel.org, otherwise I might
miss it :)

Also, you can add:
	Cc: stable <stable@kernel.org>
to the signed-off-by area of the patch, and when it is taken into
Linus's tree, the stable team will automatically get notified of it and
include it in the next stable releases without any other work needed to
be done by you.

hope this helps,

greg k-h

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