linux-kernel - Re: [PATCH RESEND v3] dma: omap-dma: add support for pause of non-cyclic transfers

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Message-ID: <d1eb15e4-7d8f-e2c0-0e27-580d3e41ac4e@ti.com>
Date:   Thu, 13 Oct 2016 13:07:53 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vignesh R <vigneshr@...com>, Vinod Koul <vinod.koul@...el.com>
CC:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: [PATCH RESEND v3] dma: omap-dma: add support for pause of
 non-cyclic transfers

On 10/10/16 17:12, Peter Ujfalusi wrote:
> On 10/10/16 15:07, Vignesh R wrote:
>> From: Sebastian Andrzej Siewior <bigeasy@...utronix.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 +
>> terminate.
> 
> Acked-by: Peter Ujfalusi <peter.ujfalusi@...com>

Can you resend the patch with corrected subject line?
dmaengine: omap-dma: ....

-- 
Péter