Re: [PATCH] spi: imx: reconfigure for PIO when DMA cannot be started

[Javier Fernandez Pastrana <javier.pastrana@linutronix.de>]

Hi Carlos,

On Wed, 24 Jun 2026 09:22:02 +0000
"Carlos Song (OSS)" <carlos.song@oss.nxp.com> wrote:

> > -----Original Message-----
> > From: Javier Fernandez Pastrana <javier.pastrana@linutronix.de>
> > Sent: Tuesday, June 23, 2026 11:33 PM
> > To: Mark Brown <broonie@kernel.org>; Frank Li <frank.li@nxp.com>;
> > Sascha Hauer <s.hauer@pengutronix.de>; Pengutronix Kernel Team
> > <kernel@pengutronix.de>; Fabio Estevam <festevam@gmail.com>; Carlos
> > Song <carlos.song@nxp.com>; linux-spi@vger.kernel.org;
> > imx@lists.linux.dev; linux-arm-kernel@lists.infradead.org;
> > linux-kernel@vger.kernel.org Cc: javier.pastrana@linutronix.de;
> > stable@vger.kernel.org Subject: [PATCH] spi: imx: reconfigure for
> > PIO when DMA cannot be started
> > 
> > [You don't often get email from javier.pastrana@linutronix.de.
> > Learn why this is important at
> > https://aka.ms/LearnAboutSenderIdentification ]
> > 
> > When spi_imx_can_dma() selects DMA, the ECSPI is configured for DMA:
> > spi_imx_setupxfer() sets CTRL.SMC and clears dynamic_burst, and
> > spi_imx_dma_transfer() programs the dynamic-burst BURST_LENGTH and
> > the SDMA watermarks.
> > 
> > If the DMA descriptor cannot be prepared
> > (dmaengine_prep_slave_single() returns NULL), the transfer is
> > failed with SPI_TRANS_FAIL_NO_START and falls back to PIO. The
> > dynamic-burst DMA path uses its own bounce buffers instead of the
> > SPI core's mapping, so xfer->{tx,rx}_sg_mapped are not set and the
> > core's DMA->PIO retry is skipped; the driver falls back to PIO
> > internally. But none of the DMA-mode configuration is undone, so
> > the PIO transfer runs with CTRL.SMC set, the wrong burst length and
> > dynamic_burst cleared, and the transferred data is corrupted.
> > 
> > This is easily hit on i.MX8MP boards that describe ECSPI DMA in the
> > device tree but run SDMA on ROM firmware (no external
> > sdma-imx7d.bin): every ECSPI DMA prepare fails. An Infineon SLB9670
> > TPM on ECSPI1 then returns shifted TPM2_GetCapability data, is
> > flagged "field failure mode", /dev/tpmrm0 is never created.
> > 
> > Mark the controller PIO-only (controller->fallback) and re-run
> > spi_imx_setupxfer() before falling back, so the ECSPI is
> > reconfigured exactly like a normal PIO transfer.
> > 
> > Fixes: faa8e404ad8e ("spi: imx: support dynamic burst length for
> > ECSPI DMA mode")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Javier Fernandez Pastrana
> > <javier.pastrana@linutronix.de> ---
> >  drivers/spi/spi-imx.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index
> > 480d1e8b281f..64c78bd79d7d 100644
> > --- a/drivers/spi/spi-imx.c
> > +++ b/drivers/spi/spi-imx.c
> > @@ -2153,6 +2153,8 @@ static int spi_imx_transfer_one(struct
> > spi_controller *controller,
> >                 ret = spi_imx_dma_transfer(spi_imx, transfer);
> >                 if (transfer->error & SPI_TRANS_FAIL_NO_START) {
> >                         spi_imx->usedma = false;
> > +                       controller->fallback = true;
> > +                       spi_imx_setupxfer(spi, transfer);  
> 
> Hi, Javier
> 
> Thank you very much for fixing this issue!
> 
> You can remove this line also: spi_imx->usedma = false;
> Because spi_imx_setupxfer() will recheck spi_imx_can_dma() and return
> false because controller->fallback = true;
> 
> How do you think about it?

Good catch. You're right, spi_imx_setupxfer() rechecks
spi_imx_can_dma(), so spi_imx->usedma = false is redundant.

I'll remove it in v2.

Thanks for reviewing!

> 
> Carlos Song
> 
> >                         if (spi_imx->target_mode)
> >                                 return
> > spi_imx_pio_transfer_target(spi, transfer);
> >                         else
> > --
> > 2.47.3
> >   
> 


Javier

-- 
Javier Fernandez Pastrana
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