Re: [PATCH 4/4] spi: spi-fsl-dspi: Report FIFO overflows as errors

James Clark
2025-06-11T14:40:43Z

On 10/06/2025 10:52 pm, Vladimir Oltean wrote:
> On Mon, Jun 09, 2025 at 04:32:41PM +0100, James Clark wrote:
>> In target mode, the host sending more data than can be consumed would be
>> a common problem for any message exceeding the FIFO or DMA buffer size.
>> Cancel the whole message as soon as this condition is hit as the message
>> will be corrupted.
>>
>> Only do this for target mode in a DMA transfer because we need to add a
>> register read. In IRQ and polling modes always do it because SPI_SR was
>> already read and it might catch some host mode programming/buffer
>> management errors too.
>>
>> Signed-off-by: James Clark <james.clark@linaro.org>
>> ---
>> drivers/spi/spi-fsl-dspi.c | 31 ++++++++++++++++++++++++++++---
>> 1 file changed, 28 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
>> index e211e44e977f..75767d756496 100644
>> --- a/drivers/spi/spi-fsl-dspi.c
>> +++ b/drivers/spi/spi-fsl-dspi.c
>> @@ -228,6 +228,7 @@ struct fsl_dspi {
>> const struct fsl_dspi_devtype_data *devtype_data;
>>
>> struct completion xfer_done;
>> + int xfer_status;
>
> This is certainly simple, and simple is not bad.
>
> But based on the fact that you care about the xfer_status only when
> there's an associated dspi->cur_msg, have you considered to update
> dspi->cur_msg->status directly?
>
> You'd need to reset dspi->cur_msg to NULL at the end of
> dspi_transfer_one_message(), and then check for NULL when you update
> the transfer status.
>

That will work. I can use it for polling and DMA modes too and I think
it looks a bit better after a refactor.

>>
>> struct fsl_dspi_dma *dma;
>>
>> @@ -504,12 +505,22 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
>>
>> static void dspi_setup_accel(struct fsl_dspi *dspi);
>>
>> +static bool dspi_is_fifo_overflow(struct fsl_dspi *dspi, u32 spi_sr)
>
> Can you name this some way else, like dspi_fifo_error()? It's strange
> for a reader for this to return true on an underflow.
>

Will do

>> +{
>> + if (spi_sr & (SPI_SR_TFUF | SPI_SR_RFOF)) {
>> + dev_err(&dspi->pdev->dev, "FIFO under/overflow");
>
> Missing \n.
>
> And you should use dev_err_ratelimited(), as you don't want an external
> entity, when in target mode, to DoS you.
>

Ack

> Also, could there be individual error messages for TFUF and for RFOF?
> If you are concerned about the penalty for the error-free case, make the
> check two-level. First for all errors, then for individual errors.
>

If I was going to split them I would probably let the compiler optimize
it whichever way was best. The real reason for combining them is because
usually you get them both together. As long as the message and fifos are
configured correctly you'd always get TFUF and RFOF at the same time and
I wanted to avoid printing twice for one event.

We could have 3 different warnings, TFUF/RFOF, TFUF and RFOF but I don't
think that's useful to an end user. At that level of debugging you'd
probably have a load of other debug printfs added anyway.

>> + return true;
>> + }
>> + return false;
>> +}
>> +
>> static int dspi_dma_xfer(struct fsl_dspi *dspi)
>> {
>> struct spi_message *message = dspi->cur_msg;
>> int max_words = dspi_dma_max_datawords(dspi);
>> struct device *dev = &dspi->pdev->dev;
>> int ret = 0;
>> + u32 spi_sr;
>>
>> /*
>> * dspi->len gets decremented by dspi_pop_tx_pushr in
>> @@ -531,6 +542,12 @@ static int dspi_dma_xfer(struct fsl_dspi *dspi)
>> dev_err(dev, "DMA transfer failed\n");
>> break;
>> }
>> +
>> + if (spi_controller_is_target(dspi->ctlr)) {
>> + regmap_read(dspi->regmap, SPI_SR, &spi_sr);
>> + if (dspi_is_fifo_overflow(dspi, spi_sr))
>> + return -EIO;
>> + }
>> }
>
> Can this go within this block from dspi_next_xfer_dma_submit() instead?
>
> if (spi_controller_is_target(dspi->ctlr)) {
> wait_for_completion_interruptible(&dspi->dma->cmd_rx_complete);
> // here
> return 0;
> }
>

Makes sense yeah

>>
>> return ret;
>> @@ -918,6 +935,8 @@ static int dspi_poll(struct fsl_dspi *dspi)
>> regmap_read(dspi->regmap, SPI_SR, &spi_sr);
>> regmap_write(dspi->regmap, SPI_SR, spi_sr);
>>
>> + if (dspi_is_fifo_overflow(dspi, spi_sr))
>> + return -EIO;
>> if (spi_sr & SPI_SR_CMDTCF)
>> break;
>> } while (--tries);
>> @@ -939,8 +958,12 @@ static irqreturn_t dspi_interrupt(int irq, void *dev_id)
>> if (!(spi_sr & SPI_SR_CMDTCF))
>> return IRQ_NONE;
>>
>> - if (dspi_rxtx(dspi) == 0)
>> + if (dspi_is_fifo_overflow(dspi, spi_sr)) {
>> + WRITE_ONCE(dspi->xfer_status, -EIO);
>> + complete(&dspi->xfer_done);
>> + } else if (dspi_rxtx(dspi) == 0) {
>> complete(&dspi->xfer_done);
>> + }
>>
>> return IRQ_HANDLED;
>> }
>> @@ -1032,13 +1055,15 @@ 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 {
>> - if (dspi->irq)
>> + if (dspi->irq) {
>> + WRITE_ONCE(dspi->xfer_status, 0);
>> reinit_completion(&dspi->xfer_done);
>> -
>
> Nitpick: The blank line was doing fine here.
>

Ack

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