On Fri, Oct 14, 2016 at 10:30:47AM +0530, Vignesh R wrote:
> From: Sebastian Andrzej Siewior <bige...@linutronix.de>
> 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 +