linux-kernel - Re: [PATCHv3 08/16] staging: vme_user: provide DMA functionality

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Message-ID: <559D2C51.9080108@ge.com>
Date:	Wed, 8 Jul 2015 14:57:37 +0100
From:	Martyn Welch <martyn.welch@...com>
To:	Dmitry Kalinkin <dmitry.kalinkin@...il.com>,
	Alessio Igor Bogani <alessioigorbogani@...il.com>
CC:	<devel@...verdev.osuosl.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Igor Alekseev <igor.alekseev@...p.ru>,
	LKML <linux-kernel@...r.kernel.org>,
	Manohar Vanga <manohar.vanga@...il.com>
Subject: Re: [PATCHv3 08/16] staging: vme_user: provide DMA functionality



On 07/07/15 11:52, Dmitry Kalinkin wrote:
> The API I had in mind would have only vme_master_read and
> vme_master_write that would take absolute addresses (not relative to
> any window). These variants of access functions would then try to
> reuse any window that is already able to serve the request or wait
> for a free window and reconfigure it for the need of the request.

I'm a little concerned by the latency this might cause, especially if 
there is one device which is negatively affected by latency. Handling 
RORA interrupts would be "interesting" if all the windows were 
dynamically allocated at the time at which an interrupt came in.

Martyn

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