Re: [PATCH RESEND v3] dma: omap-dma: add support for pause of non-cyclic transfers
From: Peter Ujfalusi
Date: Thu Oct 13 2016 - 06:22:10 EST
On 10/10/16 17:12, Peter Ujfalusi wrote:
> On 10/10/16 15:07, Vignesh R wrote:
>> From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
>> This DMA driver is used by 8250-omap on DRA7-evm. There is one
>> requirement that is to pause a transfer. This is currently used on the RX
>> side. It is possible that the UART HW aborted the RX (UART's RX-timeout)
>> but the DMA controller starts the transfer shortly after.
>> Before we can manually purge the FIFO we need to pause the transfer,
>> check how many bytes it already received and terminate the transfer
>> without it making any progress.
>> From testing on the TX side it seems that it is possible that we invoke
>> pause once the transfer has completed which is indicated by the missing
>> CCR_ENABLE bit but before the interrupt has been noticed. In that case the
>> interrupt will come even after disabling it.
>> The AM572x manual says that we have to wait for the CCR_RD_ACTIVE &
>> CCR_WR_ACTIVE bits to be gone before programming it again here is the
>> drain loop. Also it looks like without the drain the TX-transfer makes
>> sometimes progress.
>> One note: The pause + resume combo is broken because after resume the
>> the complete transfer will be programmed again. That means the already
>> transferred bytes (until the pause event) will be sent again. This is
>> currently not important for my UART user because it does only pause +
> Acked-by: Peter Ujfalusi <peter.ujfalusi@xxxxxx>
Can you resend the patch with corrected subject line?
dmaengine: omap-dma: ....