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

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Date:   Tue, 22 Dec 2020 17:48:31 +0530
From:   mdalam@...eaurora.org
To:     Thara Gopinath <thara.gopinath@...aro.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 2020-12-21 23:39, Thara Gopinath wrote:
> 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 ?

Yes you are right.
We are having some register which will configure the pipe lock group.
But these registers are not exposed to non-secure world. These registers
only accessible through secure world. Currently in IPQ5018 SoC we are 
configuring
these register in secure world to configure pipe lock group.