linux-kernel - Re: [PATCH v5 2/2] Add Intel LGM soc DMA support.

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Date:   Fri, 4 Sep 2020 09:31:37 +0300
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     "Reddy, MallikarjunaX" <mallikarjunax.reddy@...ux.intel.com>,
        <dmaengine@...r.kernel.org>, <vkoul@...nel.org>,
        <devicetree@...r.kernel.org>, <robh+dt@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <andriy.shevchenko@...el.com>,
        <cheol.yong.kim@...el.com>, <qi-ming.wu@...el.com>,
        <chuanhua.lei@...ux.intel.com>, <malliamireddy009@...il.com>
Subject: Re: [PATCH v5 2/2] Add Intel LGM soc DMA support.



On 31/08/2020 11.07, Reddy, MallikarjunaX wrote:
> 
> On 8/28/2020 7:17 PM, Peter Ujfalusi wrote:
>> Hi,
>>
>> On 27/08/2020 17.41, Reddy, MallikarjunaX wrote:
>>>>>>> +
>>>>>>> +    dma_dev->device_alloc_chan_resources =
>>>>>>> +        d->inst->ops->device_alloc_chan_resources;
>>>>>>> +    dma_dev->device_free_chan_resources =
>>>>>>> +        d->inst->ops->device_free_chan_resources;
>>>>>>> +    dma_dev->device_terminate_all =
>>>>>>> d->inst->ops->device_terminate_all;
>>>>>>> +    dma_dev->device_issue_pending =
>>>>>>> d->inst->ops->device_issue_pending;
>>>>>>> +    dma_dev->device_tx_status = d->inst->ops->device_tx_status;
>>>>>>> +    dma_dev->device_resume = d->inst->ops->device_resume;
>>>>>>> +    dma_dev->device_pause = d->inst->ops->device_pause;
>>>>>>> +    dma_dev->device_config = d->inst->ops->device_config;
>>>>>>> +    dma_dev->device_prep_slave_sg =
>>>>>>> d->inst->ops->device_prep_slave_sg;
>>>>>>> +    dma_dev->device_synchronize = d->inst->ops->device_synchronize;
>>>>>>> +
>>>>>>> +    if (d->ver == DMA_VER22) {
>>>>>>> +        dma_dev->src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>>>>>>> +        dma_dev->dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>>>>>>> +        dma_dev->directions = BIT(DMA_MEM_TO_DEV) |
>>>>>>> +                      BIT(DMA_DEV_TO_MEM);
>>>>>>> +        dma_dev->residue_granularity =
>>>>>>> +                    DMA_RESIDUE_GRANULARITY_DESCRIPTOR;
>>>>>>> +    }
>>>>>> So, if version is != DMA_VER22, then you don't support any direction?
>>>>>> Why register the DMA device if it can not do any transfer?
>>>>> Only dma0 instance (intel,lgm-cdma) is used as a general purpose slave
>>>>> DMA. we set both control and datapath here.
>>>>> Other instances we set only control path. data path is taken care
>>>>> by dma
>>>>> client(GSWIP).
>>>> How the client (GSWIP) can request a channel from intel,lgm-* ? Don't
>>>> you need some capabilities for the DMA device so core can sort out the
>>>> request?
>>> client request channel by name, dma_request_slave_channel(dev, name);
>> clients should use dma_request_chan(dev, name);
>>
>> If the channel can be requested via DT or ACPI then we don't check the
>> capabilities at all, so yes, that could work.
>>
>>>>> Only thing needs to do is get the channel, set the descriptor and just
>>>>> on the channel.
>>>> How do you 'on' the channel?
>>> we on the channel in issue_pending.
>> Right.
>> Basically you only prep_slave_sg/single for the DMA_VER22? Or do you
>> that for the others w/o direction support?
>
> Yes. prep_slave_sg/single only for the DMA_VER22.

So, you place the transfers to DMA_VER22's channel

>>
>> For the intel,lgm-* DMAs you only call issue_pending() and probably
>> terminate_all?
> Yes, correct.

and issue_pending on a channel which does not have anything pending?
How client knows which of the 'only need to be ON' channel to enable
when it placed a transfer to another channel?

How would the client driver (and the IP) would be integrated with
different system DMA which have standard channel management?

If DMA_VER22 knows which intel,lgm-* it should place the transfer then
with virt-dma you can handle that just fine?

Do you have public documentation for the DMA? It sounds a bit like TI's
EDMA which is in essence is a two part  setup:
CC: Channel Controller - to submit transfers (like your DMA_VER22)
TC: Transfer Controller - it executes the transfers submitted by the CC

One CC can be backed by multiple TCs. I don't have direct control over
the TC (can not start/stop), it is controlled by the CC.

Documentation/devicetree/bindings/dma/ti-edma.txt

Or is it a different setup?

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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