linux-kernel - Re: [PATCH V10 1/1] dmaengine: amd: qdma: Add AMD QDMA driver

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Message-ID: <5e2e2539-38e0-1d3c-62c2-da986da1c68f@amd.com>
Date: Thu, 18 Apr 2024 10:35:44 -0700
From: Lizhi Hou <lizhi.hou@....com>
To: Vinod Koul <vkoul@...nel.org>
CC: <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Nishad Saraf
	<nishads@....com>, <nishad.saraf@....com>, <sonal.santan@....com>,
	<max.zhen@....com>
Subject: Re: [PATCH V10 1/1] dmaengine: amd: qdma: Add AMD QDMA driver


On 4/18/24 10:08, Vinod Koul wrote:
> On 17-04-24, 10:53, Lizhi Hou wrote:
>> On 4/17/24 10:03, Vinod Koul wrote:
>>> On 08-04-24, 11:06, Lizhi Hou wrote:
>>>
>>>>>> +static void *qdma_get_metadata_ptr(struct dma_async_tx_descriptor *tx,
>>>>>> +				   size_t *payload_len, size_t *max_len)
>>>>>> +{
>>>>>> +	struct qdma_mm_vdesc *vdesc;
>>>>>> +
>>>>>> +	vdesc = container_of(tx, typeof(*vdesc), vdesc.tx);
>>>>>> +	if (payload_len)
>>>>>> +		*payload_len = sizeof(vdesc->dev_addr);
>>>>>> +	if (max_len)
>>>>>> +		*max_len = sizeof(vdesc->dev_addr);
>>>>>> +
>>>>>> +	return &vdesc->dev_addr;
>>>>> Can you describe what metadata is being used here for?
>>>> The metadata is the device address the dma request will transfer
>>>>
>>>> data to / from.  Please see the example usage here:
>>>>
>>>> https://github.com/houlz0507/XRT-1/blob/qdma_v1_usage/src/runtime_src/core/pcie/driver/linux/xocl/subdev/qdma.c#L311
>>>>
>>>> Before dmaengine_submit(), it specifies the device address.
>>> Hmmm, why is the vaddr passed like this, why not use slave_config for
>>> this
>>>
>> This is because the hardware is capable to process multiple vdesc at one
>> kick off.
>>
>> For example, there are two pending vdesc: vd1 and vd2. If there is enough
>> free
>>
>> space in hardware queue, the vd1 and vd2 can be put in queue, and do one
>> kick off
>>
>> to transfer both vd1 and vd2.
>>
>> The destination device address of vd1 and vd2 could be any valid device
>> address.
>>
>> desc_metadata_ptr seems helpful for the per vdesc destination device
>> address.
>>
>>
>> If using slave_config, it needs to call dmaengine_slave_config() and
> That would be the right thing to do...
>
> - set parameters and call dmaengine_slave_config()
> - prep transfer for vd1 dmaengine_prep_slave_sg()
> - set parameters and call dmaengine_slave_config()
> - prep transfer for vd2 dmaengine_prep_slave_sg()
> - submit vd1
> - submit vd2
> - issue_pending
>          - you see you can issue both as you have space, so do that
>
> This should be done always to maximize the dmaengine thoroughput

Thanks for your comments. I will change this.


Lizhi

>
>> dmaengine_prep_slave_sg() with a lock protection. Is this what you would
>> recommend?
>>
>>
>> Thanks,
>>
>> Lizhi