Re: [PATCH v1 1/1] spi: dw: revisit FIFO size detection again

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, 2015-02-25 at 12:53 +0800, Axel Lin wrote:
> 2015-02-25 2:43 GMT+08:00 Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>:
> > The commit d297933cc7fc (spi: dw: Fix detecting FIFO depth) tries to fix the
> > logic of the FIFO detection based on the description on the comments. However,
> > there is a slight difference between numbers in TX Level and TX FIFO size.
> >
> > So, by specification the FIFO size would be in a range 2-256 bytes. From TX
> > Level prospective it means we can set threshold in the range 0-(FIFO size - 1)
> > bytes. Hence there are currently two issues:
> >   a) FIFO size 2 bytes is actually skipped since TX Level is 1 bit and could be
> >      either 0 or 1 byte;
> >   b) FIFO size is incorrectly decreased by 1 which already done by meaning of
> >      TX Level register.
> >
> > This patch fixes it eventually right.
> >
> > Fixes: d297933cc7fc (spi: dw: Fix detecting FIFO depth)
> > Cc: Axel Lin <axel.lin@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > ---
> >
> > Shame on me I somehow missed this when tested mentioned patch.
> >
> >  drivers/spi/spi-dw.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
> > index 0257dd1..ba9773d 100644
> > --- a/drivers/spi/spi-dw.c
> > +++ b/drivers/spi/spi-dw.c
> > @@ -494,14 +494,14 @@ static void spi_hw_init(struct device *dev, struct dw_spi *dws)
> >         if (!dws->fifo_len) {
> >                 u32 fifo;
> >
> > -               for (fifo = 2; fifo <= 256; fifo++) {
> > +               for (fifo = 1; fifo <= 256; fifo++) {
> 
> I think the upper bound of the for loop should be 255 (FIFO size - 1)
> for (fifo = 1; fifo <= 255; fifo++) {
> so if writting 255 to DW_SPI_TXFLTR success, fifo_len is 256.
> 
> no need to test writing 256 to  DW_SPI_TXFLTR.


Yes, I even just retested carefully.
I will change to < 256 and keep your Reviewed-by tag in v2, hope it's
okay.

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
Intel Finland Oy

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