linux-kernel - Re: [PATCH v3 2/2] dma: pl330: add DMA

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Date:	Wed, 11 Feb 2015 12:02:14 +0100
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	dan.j.williams@...el.com, lars@...afoo.de,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	m.szyprowski@...sung.com, k.kozlowski@...sung.com,
	kyungmin.park@...sung.com, l.czerwinski@...sung.com,
	padma.kvr@...il.com
Subject: Re: [PATCH v3 2/2] dma: pl330: add DMA_PAUSE feature

On 02/11/2015 01:24 AM, Vinod Koul wrote:
> On Wed, Dec 10, 2014 at 11:55:18AM +0100, Robert Baldyga wrote:
>> DMA_PAUSE command is used for halting DMA transfer on chosen channel.
>> It can be useful when we want to safely read residue before terminating
>> all requests on channel. Otherwise there can be situation when some data
>> is transferred before channel termination but after reading residue,
>> which obviously results with data loss. To avoid this situation we can
>> pause channel, read residue and then terminate all requests.
>> This scenario is common, for example, in serial port drivers.
> And where is the resume here? Also this needs rebase
> 

We can't have resume on this hardware. It's in comment. DMA_PAUSE
feature is added only to freeze channel state before its termination to
allow safe residue read.

BTW I was almost sure that you have applied these patches to your tree
about two months ago. In mainline kernel there is already samsung serial
driver using DMA, which wouldn't work without these changes. Hence it
would be great to have my patches applied ASAP. I will send v4 today.

Thanks,
Robert Baldyga
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