Re: [PATCH FIX] spi: bcm-qspi: switch back to reading flash using smaller chunks

[Kamal Dasu <kdasu.kdev@xxxxxxxxx>]

Rafal,

"switching back to 256bytes is not helping us understanding what's
going on here.. "

The read take a different path and use hw acceleration. . It is to do
with the BSPI_RAF buffer size. I think  it's safe to keep it at 256
and will not impact performance either.

Kamal
On Fri, Oct 12, 2018 at 5:30 AM Boris Brezillon
<boris.brezillon@xxxxxxxxxxx> wrote:
>
> On Thu, 11 Oct 2018 09:42:17 +0200
> Rafał Miłecki <zajec5@xxxxxxxxx> wrote:
>
> > From: Rafał Miłecki <rafal@xxxxxxxxxx>
> >
> > Fixing/optimizing bcm_qspi_bspi_read() performance introduced two
> > changes:
> > 1) It added a loop to read all requested data using multiple BSPI ops.
> > 2) It bumped max size of a single BSPI block request from 256 to 512 B.
> >
> > The later change resulted in occasional BSPI timeouts causing a
> > regression.
> >
> > For some unknown reason hardware doesn't always handle reads as expected
> > when using 512 B chunks. In such cases it may happen that BSPI returns
> > amount of requested bytes without the last 1-3 ones. It provides the
> > remaining bytes later but doesn't raise an interrupt until another LR
> > start.
> >
> > Switching back to 256 B reads fixes that problem and regression.
>
> Kamal, can you help Rafal with this issue? I mean, even if it seems to
> solve the problem, switching back to 256bytes is not helping us
> understanding what's going on here.
>
> >
> > Fixes: 345309fa7c0c ("spi: bcm-qspi: Fix bcm_qspi_bspi_read() performance")
> > Signed-off-by: Rafał Miłecki <rafal@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx # 4.11+
> > ---
> > This fixes a regression I reported 2,5 months ago in the e-mail thread:
> > bcm-qspi: unstable bspi mode since the 345309fa7c0c ("spi: bcm-qspi: Fix bcm_qspi_bspi_read() performance")
> > ---
> >  drivers/spi/spi-bcm-qspi.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/spi/spi-bcm-qspi.c b/drivers/spi/spi-bcm-qspi.c
> > index eb3d67f01e8c..584bcb018a62 100644
> > --- a/drivers/spi/spi-bcm-qspi.c
> > +++ b/drivers/spi/spi-bcm-qspi.c
> > @@ -89,7 +89,7 @@
> >  #define BSPI_BPP_MODE_SELECT_MASK            BIT(8)
> >  #define BSPI_BPP_ADDR_SELECT_MASK            BIT(16)
> >
> > -#define BSPI_READ_LENGTH                     512
> > +#define BSPI_READ_LENGTH                     256
> >
> >  /* MSPI register offsets */
> >  #define MSPI_SPCR0_LSB                               0x000
>