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

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Date:   Tue, 12 Jan 2021 15:00:02 +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, mdalam=codeaurora.org@...eaurora.org
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit
 support

On 2020-12-22 17:48, mdalam@...eaurora.org wrote:
> 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.

ping! Is there any update on this ? Do you need any further info ?