linux-kernel - Re: [PATCH v2 3/4] DMA: PL330: Balance module remove function with probe

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Message-ID: <1351485943.7077.30.camel@vkoul-udesk3>
Date:	Mon, 29 Oct 2012 10:15:43 +0530
From:	Vinod Koul <vkoul@...radead.org>
To:	Inderpal Singh <inderpal.singh@...aro.org>
Cc:	vinod.koul@...el.com, linux-samsung-soc@...r.kernel.org,
	linux-kernel@...r.kernel.org, jassisinghbrar@...il.com,
	boojin.kim@...sung.com, patches@...aro.org, kgene.kim@...sung.com
Subject: Re: [PATCH v2 3/4] DMA: PL330: Balance module remove function with
 probe

On Sat, 2012-10-27 at 15:50 +0530, Inderpal Singh wrote:
> Hi Vinod,
> 
> On 26 October 2012 10:15, Vinod Koul <vkoul@...radead.org> wrote:
> > On Thu, 2012-10-25 at 16:53 +0530, Inderpal Singh wrote:
> >>
> >> This code will get executed only in case of force removal of the
> >> module which was discussed in the first version of the patch at [1].
> >> Now, if we do not have to think about force removal then this patch
> >> will go back to the first version.
> > But why are you doing force removal of driver even when client is
> > holding a reference to you.
> >
> > What happens when client finally tries to free the channel?
> Since we return EBUSY so forced removal won't succeed. Client can free
> the channel eventually.
And that is my concern. You have forcefully removed the dma module.
What happens then? How will the free calll get executed, wont you hit a
panic.
> 
> >
> > What is the problem you are trying to solve?
> >>
> 
> There was a long discussion about it in the first version of the
> patch. Allow me to explain it to you.
> 
> The existing driver does DMA_TERMINATE_ALL and frees resources for all
> the channels in the _remove function.
Which for starters may not be right thing to do. Shouldn't you first
make sure client has freed all references to your driver and then only
remove. Freeing resources in .remove without keeping client in sync
doesn't sound to be good idea to me.

>  The first version of patch
> removed this flushing and freeing of channel resources because they
> are not getting allocated in the probe. Jassi pointed out that manual
> flushing is needed if a force removal happens and some client is
> queued. Then it was agreed that flushing is not needed, instead we
> should return EBUSY if client is queued on some channel (this will
> happen only in force removal case). Hence this additional check in v2
> version so that force removal does not succeeds if any client is
> queued.
> 
> If you think force removal is not a practical scenario and we should
> not be bothering about it, this check can be removed and the patch
> will go back to first version which just removes flushing and freeing
> of channels beacues they are not getting allocated in probe.
> 
> Let me know your view.
> 
> Regards,
> Inder
> 
> 
> >> Let me know your view.
> >>
> >> [1] https://patchwork.kernel.org/patch/1503171/
> >>
> >
> >
> > --
> > Vinod Koul
> > Intel Corp.
> >


-- 
Vinod Koul
Intel Corp.

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