Messages in this thread |  | | Subject | Re: [PATCH] iio: adc: stm32-adc: Use dma_request_chan() instead dma_request_slave_channel() | From | Fabrice Gasnier <> | Date | Mon, 6 Jan 2020 11:25:11 +0100 |
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On 12/23/19 4:42 PM, Jonathan Cameron wrote: > On Tue, 17 Dec 2019 09:51:53 +0200 > Peter Ujfalusi <peter.ujfalusi@ti.com> wrote: > >> dma_request_slave_channel() is a wrapper on top of dma_request_chan() >> eating up the error code. >> >> By using dma_request_chan() directly the driver can support deferred >> probing against DMA. >> >> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com> > Hi Peter, > > Change looks sensible to me, but I'd like to leave a little longer > for others to look at this. > > Give me a poke if I seem to have lost it by the end of the first > week in Jan. > > Thanks, > > Jonathan > >> --- >> drivers/iio/adc/stm32-adc.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c >> index 3b291d72701c..5dab23f1fdee 100644 >> --- a/drivers/iio/adc/stm32-adc.c >> +++ b/drivers/iio/adc/stm32-adc.c >> @@ -1746,9 +1746,15 @@ static int stm32_adc_dma_request(struct iio_dev *indio_dev) >> struct dma_slave_config config; >> int ret; >> >> - adc->dma_chan = dma_request_slave_channel(&indio_dev->dev, "rx"); >> - if (!adc->dma_chan) >> + adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx"); >> + if (IS_ERR(adc->dma_chan)) { >> + if (PTR_ERR(adc->dma_chan) == -EPROBE_DEFER) >> + return -EPROBE_DEFER;
Hi Peter,
Thanks for the patch and sorry for the late reply.
I'd rather prefer to check explicitly for -ENODEV (as the DMA is optional) to use the IRQ mode and treat all other codes (including EPROBE_DEFER) as errors.
Rationale is: This can hide other errors e.g. like all DMA channels are busy/reserved for other usage. So the user may wrongly think it's probing the driver, with DMA. This may be a corner case, but still... DMA channels are assigned via device tree. I'd rather prefer to avoid depending of runtime (probe ordering) in such a case.
Can you update the patch considering this ?
Please find here an alternate proposal:
adc->dma_chan = dma_request_chan(&indio_dev->dev, "rx"); if (IS_ERR(adc->dma_chan)) { if (PTR_ERR(adc->dma_chan) != -ENODEV) return PTR_ERR(adc->dma_chan);
/* DMA is optional: fall back to IRQ mode */ adc->dma_chan = NULL; return 0; }
Best regards, Fabrice
>> + >> + /* Ignore errors to fall back to IRQ mode */ >> + adc->dma_chan = NULL; >> return 0; >> + } >> >> adc->rx_buf = dma_alloc_coherent(adc->dma_chan->device->dev, >> STM32_DMA_BUFFER_SIZE, >
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