Re: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

[Dmitry Osipenko <digetx@gmail.com>]

31.01.2022 12:09, Akhil R пишет:
>> В Mon, 31 Jan 2022 04:25:14 +0000
>> Akhil R <akhilrajeev@nvidia.com> пишет:
>>
>>>> 30.01.2022 19:34, Akhil R пишет:
>>>>>> 29.01.2022 19:40, Akhil R пишет:
>>>>>>> +static int tegra_dma_device_pause(struct dma_chan *dc) {
>>>>>>> +     struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
>>>>>>> +     unsigned long wcount, flags;
>>>>>>> +     int ret = 0;
>>>>>>> +
>>>>>>> +     if (!tdc->tdma->chip_data->hw_support_pause)
>>>>>>> +             return 0;
>>>>>>
>>>>>> It's wrong to return zero if pause unsupported, please see what
>>>>>> dmaengine_pause() returns.
>>>>>>
>>>>>>> +
>>>>>>> +     spin_lock_irqsave(&tdc->vc.lock, flags);
>>>>>>> +     if (!tdc->dma_desc)
>>>>>>> +             goto out;
>>>>>>> +
>>>>>>> +     ret = tegra_dma_pause(tdc);
>>>>>>> +     if (ret) {
>>>>>>> +             dev_err(tdc2dev(tdc), "DMA pause timed out\n");
>>>>>>> +             goto out;
>>>>>>> +     }
>>>>>>> +
>>>>>>> +     wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
>>>>>>> +     tdc->dma_desc->bytes_xfer +=
>>>>>>> +                     tdc->dma_desc->bytes_req - (wcount * 4);
>>>>>>
>>>>>> Why transfer is accumulated?
>>>>>>
>>>>>> Why do you need to update xfer size at all on pause?
>>>>>
>>>>> I will verify the calculation. This looks correct only for single
>>>>> sg transaction.
>>>>>
>>>>> Updating xfer_size is added to support drivers which pause the
>>>>> transaction and read the status before terminating.
>>>>> Eg.
>>>>
>>>> Why you couldn't update the status in tegra_dma_terminate_all()?
>>> Is it useful to update the status in terminate_all()? I assume the
>>> descriptor Is freed in vchan_dma_desc_free_list() or am I getting it
>>> wrong?
>>
>> Yes, it's not useful. Then you only need to fix the tx_status() and
>> don't touch dma_desc on pause.
> If the bytes_xfer is updated in tx_status(), I suppose 
> DMA_RESIDUE_GRANULARITY_BURST can be kept as is, correct?

You don't need to update bytes_xfer in tx_status(). Please see Tegra20
DMA driver for the example, which supports GRANULARITY_BURST properly.