linux-kernel - Re: [PATCH v4 2/3] dmaengine: add peripheral configuration

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Date:   Fri, 9 Oct 2020 13:45:55 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     <dmaengine@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] dmaengine: add peripheral configuration

Hi Vinod,

On 09/10/2020 13.30, Vinod Koul wrote:
> Hi Peter,
> 
> On 09-10-20, 12:04, Peter Ujfalusi wrote:
>> On 08/10/2020 15.31, Vinod Koul wrote:
>>> Some complex dmaengine controllers have capability to program the
>>> peripheral device, so pass on the peripheral configuration as part of
>>> dma_slave_config
>>>
>>> Signed-off-by: Vinod Koul <vkoul@...nel.org>
>>> ---
>>>  include/linux/dmaengine.h | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>>> index 6fbd5c99e30c..a15dc2960f6d 100644
>>> --- a/include/linux/dmaengine.h
>>> +++ b/include/linux/dmaengine.h
>>> @@ -418,6 +418,9 @@ enum dma_slave_buswidth {
>>>   * @slave_id: Slave requester id. Only valid for slave channels. The dma
>>>   * slave peripheral will have unique id as dma requester which need to be
>>>   * pass as slave config.
>>> + * @peripheral_config: peripheral configuration for programming peripheral
>>> + * for dmaengine transfer
>>> + * @peripheral_size: peripheral configuration buffer size
>>>   *
>>>   * This struct is passed in as configuration data to a DMA engine
>>>   * in order to set up a certain channel for DMA transport at runtime.
>>> @@ -443,6 +446,8 @@ struct dma_slave_config {
>>>  	u32 dst_port_window_size;
>>>  	bool device_fc;
>>>  	unsigned int slave_id;
>>> +	void *peripheral_config;
>>> +	size_t peripheral_size;
>>
>> Do you foresee a need of src/dst pair of these?
>> If we do DEV_TO_DEV with different type of peripherals it is going to
>> cause issues.
> 
> Not really as the channel already has direction and this is per channel.

Yes, in case of DEV_TO_MEM or MEM_TO_DEV.

> If for any any reason subsequent txn is for different direction, I would
> expect that parameters are set again before prep_ calls

But in DEV_TO_DEV?
If we have two peripherals, both needs config:
p1_config and p2_config

What and how would one use the single peripheral_config?

If only one of them needs config, then sure, the driver can pin-point
which one the single config might apply to.

Or you chain the same type of peripheral and you would need different
config for tx and rx?

- Péter

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