linux-kernel - Re: [PATCH 7/9] ARM: edma: Don't clear EMR of channel in edma

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Date:	Tue, 30 Jul 2013 13:59:54 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Joel Fernandes <joelf@...com>
CC:	Tony Lindgren <tony@...mide.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Sricharan R <r.sricharan@...com>,
	Rajendra Nayak <rnayak@...com>,
	Lokesh Vutla <lokeshvutla@...com>,
	Matt Porter <matt@...orter.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Mark Brown <broonie@...aro.org>,
	Benoit Cousson <benoit.cousson@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Balaji TK <balajitk@...com>,
	Gururaja Hebbar <gururaja.hebbar@...com>,
	Chris Ball <cjb@...top.org>,
	Jason Kridner <jkridner@...gleboard.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>
Subject: Re: [PATCH 7/9] ARM: edma: Don't clear EMR of channel in edma_stop

On Monday 29 July 2013 06:59 PM, Joel Fernandes wrote:
> We certainly don't want error conditions to be cleared anywhere

'anywhere' is a really loaded term.

> as this will make us 'forget' about missed events. We depend on
> knowing which events were missed in order to be able to reissue them.

> This fixes a race condition where the EMR was being cleared
> by the transfer completion interrupt handler.
> 
> Basically, what was happening was:
> 
>             Missed event
>              |
>              |
>              V
> SG1-SG2-SG3-Null
>          \
>           \__TC Interrupt (Almost same time as ARM is executing
> TC interrupt handler, an event got missed and also forgotten
> by clearing the EMR).

Sorry, but I dont see how edma_stop() is coming into picture in the race
you describe?

> The EMR is ultimately being cleared by the Error interrupt
> handler once it is handled so we don't have to do it in edma_stop.

This, I agree with. edma_clean_channel() also there to re-initialize the
channel so doing it in edma_stop() certainly seems superfluous.

Thanks,
Sekhar

> 
> Signed-off-by: Joel Fernandes <joelf@...com>
> ---
>  arch/arm/common/edma.c |    1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/arm/common/edma.c b/arch/arm/common/edma.c
> index 10995b2..dec772e 100644
> --- a/arch/arm/common/edma.c
> +++ b/arch/arm/common/edma.c
> @@ -1328,7 +1328,6 @@ void edma_stop(unsigned channel)
>  		edma_shadow0_write_array(ctlr, SH_EECR, j, mask);
>  		edma_shadow0_write_array(ctlr, SH_ECR, j, mask);
>  		edma_shadow0_write_array(ctlr, SH_SECR, j, mask);
> -		edma_write_array(ctlr, EDMA_EMCR, j, mask);
>  
>  		pr_debug("EDMA: EER%d %08x\n", j,
>  				edma_shadow0_read_array(ctlr, SH_EER, j));
> 

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