linux-kernel - Re: [PATCH] dmaengine: at_xdmac: Fix wrongfull report of a channel as in use

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Message-ID: <20190123121641.GN4635@vkoul-mobl>
Date:   Wed, 23 Jan 2019 17:46:41 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Codrin.Ciubotariu@...rochip.com
Cc:     Ludovic.Desroches@...rochip.com, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: at_xdmac: Fix wrongfull report of a channel
 as in use

On 21-01-19, 14:38, Codrin.Ciubotariu@...rochip.com wrote:
> On 20.01.2019 13:04, Vinod Koul wrote:
> > Hi Codrin,
> > 
> > On 17-01-19, 16:10, Codrin.Ciubotariu@...rochip.com wrote:
> >> From: Codrin Ciubotariu <codrin.ciubotariu@...rochip.com>
> >>
> >> atchan->status is used for two things:
> >>   - pass channel interrupts status from interrupt handler to tasklet;
> >>   - channel information like whether it is cyclic or paused;
> >>
> >> Since these operations have nothing in common, this patch adds a
> >> different struct member to keep the interrupts status.
> >>
> >> Fixes a bug in which a channel is wrongfully reported as in use when
> >> trying to obtain a new descriptior for a previously used cyclic channel.
> > 
> > This looks reasonable but am unable to see how the bug is fixed. Perhaps
> > would be great to split the bug part (which can go to fixes) and remove
> > the reuse of variable as a subsequent patch..
> 
> Hi Vinod,
> 
> This patch is the fix, since it moves the operations on atchan->status, 
> in which the interrupt status register is saved, to a different member 
> (irq_status). The AT_XDMAC_CHAN_IS_CYCLIC and AT_XDMAC_CHAN_IS_PAUSED 
> bits have nothing in common with the interrupt status register.
> 
> The bug reproduces when a device_terminate_all() is called, 
> (AT_XDMAC_CHAN_IS_CYCLIC cleared on atchan->status) and then a late End 
> of Block interrupt arrives (AT_XDMAC_CIS_BIS), which sets bit 0 of 
> atchan->status. Bit 0 is also used for AT_XDMAC_CHAN_IS_CYCLIC, so when 
> a new descriptor for a cyclic transfer is created, the driver reports 
> the channel as in use:
> 
> if (test_and_set_bit(AT_XDMAC_CHAN_IS_CYCLIC, &atchan->status)) {
> 	dev_err(chan2dev(chan), "channel currently used\n");
> 	return NULL;
> }
> 
> I can send v2 if you consider the commit message misleading.

Yes please, that would be better and pls add fixes as suggested by
Ludovic along with his ack

-- 
~Vinod