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

Akhil R
2022-01-31T09:09:28Z

> 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?

Thanks,
Akhil