[PATCH] arm: atmel_qspi: fix race condition in transfer completion check

[Ramin Moussavi]

Hello Eugen

here is the updated patch

Am Mo., 14. Juli 2025 um 22:33 Uhr schrieb Eugen Hristev <
eugen.hristev at linaro.org>:

> Hello Ramin,
>
> Thank you for your patch.
>
> Can you please change the subject to have "spi: atmel_qspi: ..."
>
> On 7/13/25 19:08, Ramin Moussavi wrote:
> > In atmel_qspi_transfer(), the status register is polled with:
> >
> >   imr = QSPI_SR_INSTRE | QSPI_SR_CSR;
> >   return readl_poll_timeout(aq->regs + QSPI_SR, sr,
> >                             (sr & imr) == imr,
> >                             ATMEL_QSPI_TIMEOUT);
> >
> > However, this is racy: QSPI_SR_INSTRE can be set before QSPI_SR_CSR,
> > and will then be cleared by the read. If that happens, the condition
> > "(sr & imr) == imr" can never be true, and the function times out.
> >
> > This race condition is avoided in at91bootstrap by accumulating the
> > status bits across reads until both bits have been observed:
> >
> >   /* Poll INSTruction End and Chip Select Rise flags. */
> >   imr = (QSPI_SR_INSTRE | QSPI_SR_CSR);
> >   sr = 0;
> >   do {
> >     udelay(1);
> >     sr |= qspi_readl(qspi, QSPI_SR) & imr;
> >   } while ((--timeout) && (sr != imr));
> >
> > Update U-Boot's atmel_qspi_transfer() to use the same pattern,
> > ensuring that both flags are observed even if they are not set
> > simultaneously.
> >
> > Signed-off-by: Ramin Seyed-Mousavi <lordrasmus at gmail.com>
> > ---
> >  drivers/spi/atmel-quadspi.c | 17 +++++++++++++++--
> >  1 file changed, 15 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
> > index 8aa7a83aef4..fba32876f8f 100644
> > --- a/drivers/spi/atmel-quadspi.c
> > +++ b/drivers/spi/atmel-quadspi.c
> > @@ -616,6 +616,8 @@ static int atmel_qspi_transfer(struct atmel_qspi *aq,
> >                              const struct spi_mem_op *op, u32 offset)
> >  {
> >       u32 sr, imr;
> > +     uint32_t val = 0;
> > +     unsigned long timeout;
> >
> >       /* Skip to the final steps if there is no data */
> >       if (op->data.nbytes) {
> > @@ -636,8 +638,19 @@ static int atmel_qspi_transfer(struct atmel_qspi
> *aq,
> >
> >       /* Poll INSTruction End and Chip Select Rise flags. */
> >       imr = QSPI_SR_INSTRE | QSPI_SR_CSR;
> > -     return readl_poll_timeout(aq->regs + QSPI_SR, sr, (sr & imr) ==
> imr,
> > -                               ATMEL_QSPI_TIMEOUT);
> > +
> > +     timeout = timer_get_us() + ATMEL_QSPI_TIMEOUT;
> > +     while(1){
>
> There is a missing space, can you please run checkpatch tool and fix the
> warnings given ?
>
> > +             val |= readl( aq->regs + QSPI_SR ) & imr;
> > +             if( ( val & imr ) == imr ){
>
> Remove unnecessary brackets please, also spacing is odd
>
> > +                     return 0;
> > +             }
> > +
> > +             if ( time_after(timer_get_us(), timeout)) {
> Same here
> > +                     return -ETIMEDOUT;
> > +             }
> > +     }
> > +
> >  }
> >
> >  static int atmel_qspi_sama7g5_set_cfg(struct atmel_qspi *aq,
>
>
> Eugen
>
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