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

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Date:	Wed, 26 Sep 2012 16:25:22 +0530
From:	Inderpal Singh <inderpal.singh@...aro.org>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	boojin.kim@...sung.com, vinod.koul@...el.com, patches@...aro.org,
	kgene.kim@...sung.com
Subject: Re: [PATCH 3/3] DMA: PL330: Balance module remove function with probe

On 26 September 2012 15:02, Jassi Brar <jassisinghbrar@...il.com> wrote:
> On Wed, Sep 26, 2012 at 12:11 PM, Inderpal Singh
> <inderpal.singh@...aro.org> wrote:
>
>> How about conditionally DMA_TERMINATE_ALL and free resources like below ?
>>
>> @@ -3017,9 +3017,11 @@ static int __devexit pl330_remove(struct
>> amba_device *adev)
>>                 /* Remove the channel */
>>                 list_del(&pch->chan.device_node);
>>
>> -               /* Flush the channel */
>> -               pl330_control(&pch->chan, DMA_TERMINATE_ALL, 0);
>> -               pl330_free_chan_resources(&pch->chan);
>> +               if (pch->chan.client_count != 0) {
>> +                       /* Flush the channel */
>> +                       pl330_control(&pch->chan, DMA_TERMINATE_ALL, 0);
>> +                       pl330_free_chan_resources(&pch->chan);
>> +               }
>>         }
>>
> It is perfectly safe to flush the channels that have client_count == 0
> as well. Which is already the case.

As per my understanding, if client_count ==0, It may mean following:

1. This channel was never allocated to any client. Hence
alloc_chan_resources was not done for it.
So, no need to flush and free resources if it was never allocated at
the first place. If we free_chan_resources, it will not be balanced
against alloc_chan_resources. Scenario: insmod and then rmmod.

Or,

2. The channel was allocated to some client, alloc_chan_resource was
done, the work for the client is completed and free_chan_resources was
performed. Now  since resources have already been freed, no need to
flush and free_chan_resources again in remove.

The whole idea of this patch is to balance alloc_chan_resources and
free_chan_resources.

Thanks,
Inder
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