Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit
 support
To:     mdalam@codeaurora.org
Cc:     vkoul@kernel.org, corbet@lwn.net, agross@kernel.org,
        bjorn.andersson@linaro.org, dan.j.williams@intel.com,
        dmaengine@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        sricharan@codeaurora.org
References: <1608215842-15381-1-git-send-email-mdalam@codeaurora.org>
 <6c85436d-e064-367e-736b-951af82256c8@linaro.org>
 <9769c54acf54617a17346fea60ee38b6@codeaurora.org>
From:   Thara Gopinath <thara.gopinath@linaro.org>
Message-ID: <8c86f4db-9956-10d1-b380-a207137b50ef@linaro.org>
Date:   Mon, 21 Dec 2020 13:09:50 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <9769c54acf54617a17346fea60ee38b6@codeaurora.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


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 ?


-- 
Warm Regards
Thara