linux-kernel - Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit support

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Message-ID: <8c86f4db-9956-10d1-b380-a207137b50ef@linaro.org>
Date:   Mon, 21 Dec 2020 13:09:50 -0500
From:   Thara Gopinath <thara.gopinath@...aro.org>
To:     mdalam@...eaurora.org
Cc:     vkoul@...nel.org, corbet@....net, agross@...nel.org,
        bjorn.andersson@...aro.org, dan.j.williams@...el.com,
        dmaengine@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        sricharan@...eaurora.org
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit
 support



On 12/21/20 2:35 AM, mdalam@...eaurora.org wrote:
> On 2020-12-19 09:05, Thara Gopinath wrote:
>> On 12/17/20 9:37 AM, Md Sadre Alam wrote:
>>> This change will add support for LOCK & UNLOCK flag bit support
>>> on CMD descriptor.
>>>
>>> If DMA_PREP_LOCK flag passed in prep_slave_sg then requester of this
>>> transaction wanted to lock the DMA controller for this transaction so
>>> BAM driver should set LOCK bit for the HW descriptor.
>>>
>>> If DMA_PREP_UNLOCK flag passed in prep_slave_sg then requester of this
>>> transaction wanted to unlock the DMA controller.so BAM driver should set
>>> UNLOCK bit for the HW descriptor.
>> Hi,
>>
>> This is a generic question. What is the point of LOCK/UNLOCK with
>> allocating LOCK groups to the individual dma channels? By default
>> doesn't all channels fall in the same group. This would mean that
>> a lock does not prevent the dma controller from not executing a
>> transaction on the other channels.
>>
> 
> The Pipe Locking/Unlocking will be only on command-descriptor.
> Upon encountering a command descriptor with LOCK bit set, the BAM
> will lock all other pipes not related to the current pipe group, and keep
> handling the current pipe only until it sees the UNLOCK set then it will
> release all locked pipes.

So unless you assign pipe groups, this will not work as intended right? 
So this patch is only half of the solution. There should also be a patch 
allowing pipe groups to be assigned. Without that extra bit this patch 
does nothing , right ?


-- 
Warm Regards
Thara