linux-kernel - Re: [PATCH 2/2] dma: add Qualcomm Technologies HIDMA channel driver

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Message-ID: <56384623.80305@codeaurora.org>
Date:	Tue, 3 Nov 2015 00:29:07 -0500
From:	Sinan Kaya <okaya@...eaurora.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	dmaengine@...r.kernel.org, timur@...eaurora.org,
	cov@...eaurora.org, jcm@...hat.com,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] dma: add Qualcomm Technologies HIDMA channel driver



On 11/2/2015 3:55 PM, Arnd Bergmann wrote:
> Are you using message signaled interrupts then?
> Typically MSI guarantees
> ordering against DMA, but level or edge triggered interrupts by definition
> cannot (at least on PCI, but most other buses are the same way), because
> the DMA master has no insight into when a DMA is actually complete.
>
> If you use MSI, please add a comment to the readl_relaxed() that it
> is safe because of that, otherwise the next person who tries to debug
> a problem with your driver has to look into this.

No, using regular GIC SPI interrupts at this moment. I know that HW 
doesn't use any of the typical AHB/AXI ARM buses.

I'm familiar with how PCI endpoints works. While the first read in a 
typical PCI endpoint ISR flushes all outstanding requests traditionally 
to the destination, this concept does not apply here for this HW.

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project
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