[U-Boot] [PATCH] spi: designware_spi: Fix off-by-one for checking fifo depth

[U-Boot] [PATCH] spi: designware_spi: Fix off-by-one for checking fifo depth

[Axel Lin]

The depth could be from 2 to 256 from HW spec, so fix off-by-one for checking
fifo depth.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
---
Hi,
I don't have this hardware handy, so please test it.
 drivers/spi/designware_spi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
index 98c9f03..14d0c23 100644
--- a/drivers/spi/designware_spi.c
+++ b/drivers/spi/designware_spi.c
@@ -164,7 +164,7 @@ static void spi_hw_init(struct dw_spi_priv *priv)
 	if (!priv->fifo_len) {
 		u32 fifo;
 
-		for (fifo = 2; fifo <= 257; fifo++) {
+		for (fifo = 2; fifo <= 256; fifo++) {
 			dw_writew(priv, DW_SPI_TXFLTR, fifo);
 			if (fifo != dw_readw(priv, DW_SPI_TXFLTR))
 				break;
-- 
1.9.1

[U-Boot] [PATCH] spi: designware_spi: Fix off-by-one for checking fifo depth

[Stefan Roese]

Hi Axel,

On 19.12.2014 05:40, Axel Lin wrote:
> The depth could be from 2 to 256 from HW spec, so fix off-by-one for checking
> fifo depth.
>
> Signed-off-by: Axel Lin <axel.lin@ingics.com>
> ---
> Hi,
> I don't have this hardware handy, so please test it.
>   drivers/spi/designware_spi.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
> index 98c9f03..14d0c23 100644
> --- a/drivers/spi/designware_spi.c
> +++ b/drivers/spi/designware_spi.c
> @@ -164,7 +164,7 @@ static void spi_hw_init(struct dw_spi_priv *priv)
>   	if (!priv->fifo_len) {
>   		u32 fifo;
>
> -		for (fifo = 2; fifo <= 257; fifo++) {
> +		for (fifo = 2; fifo <= 256; fifo++) {
>   			dw_writew(priv, DW_SPI_TXFLTR, fifo);
>   			if (fifo != dw_readw(priv, DW_SPI_TXFLTR))
>   				break;

Please note that this code was not written by myself but is based on the 
Linux kernel version. And from my current understanding, this code tries 
to detect the FIFO size. So this 257 being bigger than the max value of 
256 is most likely correct. Also another 257 is a few lines below your code:

		dws->fifo_len = (fifo == 257) ? 0 : fifo;

So I don't think that we need to change this here.

BTW: It might be better to send this patch (or a question about this 256 
vs 257) to the SPI Linux mailing list. The maintainer there will have 
deeper knowledge about this issue.

Thanks,
Stefan

[U-Boot] [PATCH] spi: designware_spi: Fix off-by-one for checking fifo depth

[Axel Lin]

2014-12-19 15:35 GMT+08:00 Stefan Roese <sr@denx.de>:
> Hi Axel,
>
>
> On 19.12.2014 05:40, Axel Lin wrote:
>>
>> The depth could be from 2 to 256 from HW spec, so fix off-by-one for
>> checking
>> fifo depth.
>>
>> Signed-off-by: Axel Lin <axel.lin@ingics.com>
>> ---
>> Hi,
>> I don't have this hardware handy, so please test it.
>>   drivers/spi/designware_spi.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/spi/designware_spi.c b/drivers/spi/designware_spi.c
>> index 98c9f03..14d0c23 100644
>> --- a/drivers/spi/designware_spi.c
>> +++ b/drivers/spi/designware_spi.c
>> @@ -164,7 +164,7 @@ static void spi_hw_init(struct dw_spi_priv *priv)
>>         if (!priv->fifo_len) {
>>                 u32 fifo;
>>
>> -               for (fifo = 2; fifo <= 257; fifo++) {
>> +               for (fifo = 2; fifo <= 256; fifo++) {
>>                         dw_writew(priv, DW_SPI_TXFLTR, fifo);
>>                         if (fifo != dw_readw(priv, DW_SPI_TXFLTR))
>>                                 break;
>
>
> Please note that this code was not written by myself but is based on the
> Linux kernel version. And from my current understanding, this code tries to
> detect the FIFO size. So this 257 being bigger than the max value of 256 is
> most likely correct. Also another 257 is a few lines below your code:
>
>                 dws->fifo_len = (fifo == 257) ? 0 : fifo;

hi Stefan,

After the for loop iteration with "no-match" case, the fifo variable will be
258 in original code. So above code won't catch such case.

>
> So I don't think that we need to change this here.
>
> BTW: It might be better to send this patch (or a question about this 256 vs
> 257) to the SPI Linux mailing list. The maintainer there will have deeper
> knowledge about this issue.

Well, I'll send similar patch for linux driver for review (in spi maillist).
Thanks.