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Date:   Tue, 12 Jan 2021 15:00:02 +0530
From:   mdalam@codeaurora.org
To:     Thara Gopinath <thara.gopinath@linaro.org>
Cc:     vkoul@kernel.org, corbet@lwn.net, agross@kernel.org,
        bjorn.andersson@linaro.org, dan.j.williams@intel.com,
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        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        sricharan@codeaurora.org, mdalam=codeaurora.org@codeaurora.org
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit
 support
In-Reply-To: <11f538a697de934551bcec5036d7fb17@codeaurora.org>
References: <1608215842-15381-1-git-send-email-mdalam@codeaurora.org>
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 <9769c54acf54617a17346fea60ee38b6@codeaurora.org>
 <8c86f4db-9956-10d1-b380-a207137b50ef@linaro.org>
 <11f538a697de934551bcec5036d7fb17@codeaurora.org>
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On 2020-12-22 17:48, mdalam@codeaurora.org wrote:
> On 2020-12-21 23:39, Thara Gopinath wrote:
>> On 12/21/20 2:35 AM, mdalam@codeaurora.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 ?