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

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Date:	Sun, 1 Nov 2015 15:27:06 -0500
From:	Sinan Kaya <okaya@...eaurora.org>
To:	Timur Tabi <timur@...eaurora.org>, Arnd Bergmann <arnd@...db.de>
Cc:	dmaengine@...r.kernel.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 11/1/2015 3:21 PM, Timur Tabi wrote:
> Sinan Kaya wrote:
>> However, after issuing the command; I still need to wait some amount of
>> time until hardware acknowledges the commands like reset/enable/disable.
>> These are relatively faster operations happening in microseconds. That's
>> why, I have mdelay there.
>
> Can you use readl_poll_timeout()?
>
Yes, I'm changing them to readl_poll_timeout after looking at the 
workqueue vs. expected delay requirements. I decided to stick with 
polled read.

First, I missed the point here that mdelay is discouraged.
https://www.kernel.org/doc/Documentation/timers/timers-howto.txt

According to same document, msleep can sleep up to 20ms which is not 
what I want.

This code is trying to sleep 10ms maximum and treating longer durations 
as failures.

readl_poll_timeout calls usleep_range that seems to satisfy what I'm 
looking for.

-- 
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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