[PATCH] mtd: cqspi: Wait for transfer completion

[Pratyush Yadav]

Hi Marek,

On 25/10/21 10:25PM, Marek Vasut wrote:
> On 10/25/21 9:53 PM, Pratyush Yadav wrote:
> > On 08/10/21 06:06PM, Jagan Teki wrote:
> > > On Wed, Sep 15, 2021 at 2:05 PM Marek Vasut <marex at denx.de> wrote:
> > > > 
> > > > On 9/15/21 10:28 AM, Pratyush Yadav wrote:
> > > > > On 14/09/21 08:22PM, Marek Vasut wrote:
> > > > > > On 9/14/21 7:42 PM, Pratyush Yadav wrote:
> > > > > > > On 14/09/21 05:22AM, Marek Vasut wrote:
> > > > > > > > Wait for the read/write transfer finish bit get actually cleared,
> > > > > > > > this does not happen immediately on at least SoCFPGA Gen5.
> > > > > > > > 
> > > > > > > > Signed-off-by: Marek Vasut <marex at denx.de>
> > > > > > > > Cc: Jagan Teki <jagan at amarulasolutions.com>
> > > > > > > > Cc: Vignesh R <vigneshr at ti.com>
> > > > > > > > Cc: Pratyush Yadav <p.yadav at ti.com>
> > > > > > > > ---
> > > > > > > >     drivers/spi/cadence_qspi_apb.c | 17 +++++++++++++++++
> > > > > > > >     1 file changed, 17 insertions(+)
> > > > > > > > 
> > > > > > > > diff --git a/drivers/spi/cadence_qspi_apb.c b/drivers/spi/cadence_qspi_apb.c
> > > > > > > > index 429ee335db6..2cdf4c9c9f8 100644
> > > > > > > > --- a/drivers/spi/cadence_qspi_apb.c
> > > > > > > > +++ b/drivers/spi/cadence_qspi_apb.c
> > > > > > > > @@ -858,6 +858,14 @@ cadence_qspi_apb_indirect_read_execute(struct cadence_spi_plat *plat,
> > > > > > > >             writel(CQSPI_REG_INDIRECTRD_DONE,
> > > > > > > >                    plat->regbase + CQSPI_REG_INDIRECTRD);
> > > > > > > > +  /* Check indirect done status */
> > > > > > > > +  ret = wait_for_bit_le32(plat->regbase + CQSPI_REG_INDIRECTRD,
> > > > > > > > +                          CQSPI_REG_INDIRECTRD_DONE, 0, 10, 0);
> > > > > > > > +  if (ret) {
> > > > > > > > +          printf("Indirect read clear completion error (%i)\n", ret);
> > > > > > > > +          goto failrd;
> > > > > > > > +  }
> > > > > > > > +
> > > > > > > 
> > > > > > > Huh, this is strange. I would expect the bit to clear immediately since
> > > > > > > it doesn't really do any operation on the flash. How long does it
> > > > > > > usually take to clear? If you don't wait for it to clear does anything
> > > > > > > break?
> > > > > > 
> > > > > > Often it does clear immediately, but there were a few odd cases where it did
> > > > > > not happen right away, in which case I had transfer corruption.
> > > > > 
> > > > > By "transfer corruption" do you mean the current transfer gets corrupted
> > > > > or the next one?
> > > > > 
> > > > > We get here _after_ the transfer is completed and this bit should have
> > > > > little to do with the data received. If the current transfer fails then
> > > > > I suspect something else might be going wrong the this is just a symptom
> > > > > of the problem.
> > > > 
> > > > As far as I recall, the problem was triggered when using UBI on the SPI
> > > > NOR, so that could very well be the next transfer.
> > > 
> > > Any further decisions here? shall I take it or v2?
> > 
> > I think we need more information here. I don't see why checking this bit
> > would interfere with the current transfer since that is already finished
> > by the time we get here. If it is the next transfer then this might just
> > be a symptom and the real problem might be somewhere else.
> 
> What additional information do you need ?

Sorry for the late reply. I dropped the ball on this one.

The additional information I needed was to know what exactly happens if 
we don't wait for this bit to be cleared. Does the _current_ transfer go 
though fine? If it does, what gets corrupted in the next transfer? Do 
you only get partial data? Do you get garbage data? Do you get no data 
at all?

All this information would be useful for understanding if this fix is 
the right one, and if so why it is the right one.

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.