Re: [PATCH v3 1/6] spi: spi-fsl-dspi: Clear completion counter before initiating transfer

[James Clark]

On 24/06/2025 4:58 pm, Frank Li wrote:
> On Tue, Jun 24, 2025 at 11:35:31AM +0100, James Clark wrote:
> > In target mode, extra interrupts can be received between the end of a
> > transfer and halting the module if the host continues sending more data.
> > If the interrupt from this occurs after the reinit_completion() then the
> > completion counter is left at a non-zero value. The next unrelated
> > transfer initiated by userspace will then complete immediately without
> > waiting for the interrupt or writing to the RX buffer.
> >
> > Fix it by resetting the counter before the transfer so that lingering
> > values are cleared. This is done after clearing the FIFOs and the
> > status register but before the transfer is initiated, so no interrupts
> > should be received at this point resulting in other race conditions.
> >
> > Fixes: 4f5ee75ea171 ("spi: spi-fsl-dspi: Replace interruptible wait queue with a simple completion")
> > Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> > ---
> >   drivers/spi/spi-fsl-dspi.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
> > index 04c88d090c4d..744dfc561db2 100644
> > --- a/drivers/spi/spi-fsl-dspi.c
> > +++ b/drivers/spi/spi-fsl-dspi.c
> > @@ -1122,11 +1122,19 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
> >   		if (dspi->devtype_data->trans_mode == DSPI_DMA_MODE) {
> >   			status = dspi_dma_xfer(dspi);
> >   		} else {
> > +			/*
> > +			 * Reset completion counter to clear any extra
> > +			 * complete()s from spurious interrupts that may have
> > +			 * happened after the last message's completion but
> > +			 * before the module was fully in stop mode.
> > +			 */
>
> I think you change is correct. reinit_completion() should be called before
> dspi_fifo_write().
>
> comments is quite confused. how about below comments?
>
> /*
>   * Reinitialize the completion before transferring data to avoid the case where
>   * it might remain in the done state due to a spurious interrupt from a previous
>   * transfer. This could falsely signal that the current transfer has completed.
>   */
>
> Frank

Will do

> > +			if (dspi->irq)
> > +				reinit_completion(&dspi->xfer_done);
> > +
> >   			dspi_fifo_write(dspi);
> >
> >   			if (dspi->irq) {
> >   				wait_for_completion(&dspi->xfer_done);
> > -				reinit_completion(&dspi->xfer_done);
> >   			} else {
> >   				do {
> >   					status = dspi_poll(dspi);
> >
> > --
> > 2.34.1