[PATCH V5 2/9] dmaengine: bcm2835-dma: add suspend/resume pm support

[Stefan Wahren]

Hi Vinod,

Am 02.12.24 um 17:52 schrieb Vinod Koul:
> On 25-10-24, 12:36, Stefan Wahren wrote:
>> bcm2835-dma provides the service to others, so it should
>> suspend late and resume early.
>>
>> Signed-off-by: Stefan Wahren <wahrenst at gmx.net>
>> ---
>>   drivers/dma/bcm2835-dma.c | 30 ++++++++++++++++++++++++++++++
>>   1 file changed, 30 insertions(+)
>>
>> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
>> index e1b92b4d7b05..647dda9f3376 100644
>> --- a/drivers/dma/bcm2835-dma.c
>> +++ b/drivers/dma/bcm2835-dma.c
>> @@ -875,6 +875,35 @@ static struct dma_chan *bcm2835_dma_xlate(struct of_phandle_args *spec,
>>   	return chan;
>>   }
>>
>> +static int bcm2835_dma_suspend_late(struct device *dev)
>> +{
>> +	struct bcm2835_dmadev *od = dev_get_drvdata(dev);
>> +	struct bcm2835_chan *c, *next;
>> +
>> +	list_for_each_entry_safe(c, next, &od->ddev.channels,
>> +				 vc.chan.device_node) {
>> +		void __iomem *chan_base = c->chan_base;
>> +
>> +		if (readl(chan_base + BCM2835_DMA_ADDR)) {
>> +			dev_warn(dev, "Suspend is prevented by chan %d\n",
>> +				 c->ch);
>> +			return -EBUSY;
>> +		}
> Can you help understand how this helps by logging... we are not adding
> anything except checking this and resume is NOP as well!
My intention of this patch is just to make sure, that no DMA transfer is
in progress during late_suspend. So i followed the implementation of
fsldma.c

Additionally i added this warning mostly to know if this ever occurs.
But i wasn't able to trigger.

Should i drop the warning and make resume callback = NULL?

Best regards