linux-kernel - Re: [PATCH] dmaengine: qcom_hidma: release the descriptor before the callback

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Message-ID: <6151fe21-3c48-e691-1c99-bafd3cc699e6@codeaurora.org>
Date:   Mon, 22 Aug 2016 09:27:04 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     Vinod Koul <vinod.koul@...el.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-arm-msm@...r.kernel.org, timur@...eaurora.org,
        linux-kernel@...r.kernel.org,
        Christopher Covington <cov@...eaurora.org>,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dmaengine: qcom_hidma: release the descriptor before the
 callback

On 8/22/2016 2:08 AM, Vinod Koul wrote:
> On Fri, Aug 19, 2016 at 01:21:34PM -0400, Sinan Kaya wrote:
>> On 8/19/2016 1:02 PM, Vinod Koul wrote:
>>> On Fri, Aug 19, 2016 at 07:13:43AM -0400, okaya@...eaurora.org wrote:
>>>> On 2016-08-19 01:52, Vinod Koul wrote:
>>>>> On Thu, Aug 18, 2016 at 11:48:52PM -0400, Sinan Kaya wrote:
>>>>>> On 8/18/2016 11:42 PM, Vinod Koul wrote:
>>>>>>> On Thu, Aug 18, 2016 at 11:26:28PM -0400, Sinan Kaya wrote:
>>>>>>>> On 8/18/2016 10:48 PM, Vinod Koul wrote:
>>>>>>>>>> Keep a size limited list with error cookies and flush them in terminate all?
>>>>>>>>> I think so, terminate_all anyway cleans up the channel. Btw what is the
>>>>>>>>> behaviour on error? Do you terminate or somthing else?
>>>>>>>>>
>>>>>>>>
>>>>>>>> On error, I flush all outstanding transactions with an error code and I reset
>>>>>>>> the channel. After the reset, the DMA channel is functional again. The client
>>>>>>>> doesn't need to shutdown anything.
>>>>>>>
>>>>>>> You mean from the client context or driver?
>>>>>>>
>>>>>>
>>>>>> The client doesn't need to call device_free_chan_resources and
>>>>>> device_terminate_all
>>>>>> to be specific. Client can certainly call these if it needs to
>>>>>> but it is not
>>>>>> required to recover the channel.
>>>>>
>>>>> You didn't answer my question!
>>>>>
>>>>> On error you said you flush, so who does that?
>>>>
>>>> This is done by the driver in interrupt context when an error
>>>> interrupt is received. All transactions are posted and hw is reset.
>>>
>>> Hmmm, waht about the txn which are pending? DO you clear them..?
>>>
>>
>> Yes, I clear both pending and active transactions. 
> 
> Okay, in that case your can consider below:
> 
> 1. dmaengine asserts error interrupt
> 2. Driver receives and mark's the txn as error
> 3. Driver completes the txn and intimates the client. No further
>    submissions. Drop the locks before calling callback, as subsequent
>    processing by client maybe in callback thread.
> 4. Client invokes status and you can return error
> 5. On error, client calls terminate_all. You can reset channel, free all
>    descriptors in the active, pending and completed lists
> 6. Client prepares new txn and so on..


Just to be clear, you are telling me not to accept any new transactions until
terminate_all is called, right?

> 
> Thanks
> 


-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.