linux-kernel - Re: [PATCH v2 1/3] dmaengine: add DMA_PREP

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Date:   Mon, 31 Jul 2017 09:35:53 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Vinod Koul <vinod.koul@...el.com>,
        Abhishek Sahu <absahu@...eaurora.org>
Cc:     "andy.gross@...aro.org" <andy.gross@...aro.org>,
        "david.brown@...aro.org" <david.brown@...aro.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-soc@...r.kernel.org" <linux-soc@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] dmaengine: add DMA_PREP_CMD for non-Data
 descriptors.



On 07/31/2017 05:34 AM, Vinod Koul wrote:
> On Fri, Jul 28, 2017 at 09:38:56PM +0530, Abhishek Sahu wrote:
>> On 2017-07-19 17:48, Abhishek Sahu wrote:
>>> On 2017-07-19 15:37, Vinod Koul wrote:
>>>> On Mon, Jun 26, 2017 at 06:19:27PM +0530, Abhishek Sahu wrote:
>>>>> Some of the DMA controllers are capable of issuing the commands
>>>>> to peripheral by the DMA. These commands can be list of register
>>>>> reads/writes and its different from normal data reads/writes.
>>>>> This patch adds new flag DMA_PREP_CMD in DMA API which tells
>>>>> the driver that the data passed to DMA API is in command format
>>>>> and DMA driver will form descriptor in the required format.
>>>>>
>>>>> This flag can be used by any DMA controller driver which requires
>>>>> special handling for non-Data descriptors.
>>>>
>>>> Please add Documentation for this new flag in
>>>> Documentation/dmaengine/provider.txt
>>>>
>>>
>>> Sure. I will add update the documentation in v3.
>>>
>>>>>
>>>>> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
>>>>> ---
>>>>> include/linux/dmaengine.h | 3 +++
>>>>> 1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>>>>> index 5336808..bbc297e 100644
>>>>> --- a/include/linux/dmaengine.h
>>>>> +++ b/include/linux/dmaengine.h
>>>>> @@ -186,6 +186,8 @@ struct dma_interleaved_template {
>>>>>  *  on the result of this operation
>>>>>  * @DMA_CTRL_REUSE: client can reuse the descriptor and submit again
>>>>> till
>>>>>  *  cleared or freed
>>>>> + * @DMA_PREP_CMD: tell the driver that the data passed to DMA API is
>>>>> in command
>>>>> + *  format and it will be used for configuring the peripheral
>>>>> registers.
>>>>
>>>> Can you explain what is command format..?
>>>>
>>>
>>> The command format is not generic and its format will be dependent
>>> upon DMA engine. The client drivers will give data in its own
>>> command formats and this flag will be passed to DMA API’s to do
>>> the parsing according to its own command format.
>>>
>>> Currently this flag description and name is inclined towards
>>> Qualcomm BAM DMA command flag. We want to make this flag as
>>> generic one so require your suggestion regarding this.
>>> Will renaming this flag as DMA_PREP_NON_DATA or
>>> DMA_PREP_CUSTOM make it more generic?
>>>
>>
>>  can we use same flag name DMA_PREP_CMD or should we
>>  go for some other name?
> 
> Are you asking for using DMA_PREP_CMD, for that I think should be ok
> 
> If you asking about adding a new flag with DMA_PREP_CMD, then it would no

Vinod, I wonder if we should introduce a DMA_PREP_CUSTOM flag and then
reserve X number of upper flag bits to vendor specified that only they
care about. That way they can define whatever they want in the upper
bits if they need it.


> 
>>
>>>>>  */
>>>>> enum dma_ctrl_flags {
>>>>> 	DMA_PREP_INTERRUPT = (1 << 0),
>>>>> @@ -195,6 +197,7 @@ enum dma_ctrl_flags {
>>>>> 	DMA_PREP_CONTINUE = (1 << 4),
>>>>> 	DMA_PREP_FENCE = (1 << 5),
>>>>> 	DMA_CTRL_REUSE = (1 << 6),
>>>>> +	DMA_PREP_CMD = (1 << 7),
>>>>> };
>>>>>
>>
>>
>> -- 
>> Abhishek Sahu
>