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

Akhil R
2022-01-30T16:43:49Z

> 30.01.2022 13:26, Dmitry Osipenko пишет:
> > 30.01.2022 13:05, Dmitry Osipenko пишет:
> >> Still nothing prevents interrupt handler to fire during the pause.
> >>
> >> What you actually need to do is to disable/enable interrupt. This
> >> will prevent the interrupt racing and then pause/resume may look like this:
> >
> > Although, seems this won't work, unfortunately. I see now that
> > device_pause() doesn't have might_sleep().
> >
>
> Ah, I see now that the pause/unpause is actually a separate control and doesn't
> conflict with "start next transfer".
>
> So you just need to set/unset the pause under lock. And don't touch
> tdc->dma_desc. That's it.
>
> static int tegra_dma_device_pause(struct dma_chan *dc) {
> struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> unsigned long flags;
> u32 val;
>
> if (!tdc->tdma->chip_data->hw_support_pause)
> return -ENOSYS;
>
> spin_lock_irqsave(&tdc->vc.lock, flags);
>
> val = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSRE);
> val |= TEGRA_GPCDMA_CHAN_CSRE_PAUSE;
> tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSRE, val);
>
> spin_unlock_irqrestore(&tdc->vc.lock, flags);
>
> return 0;
> }
>
> static int tegra_dma_device_resume(struct dma_chan *dc) {
> struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> unsigned long flags;
> u32 val;
>
> if (!tdc->tdma->chip_data->hw_support_pause)
> return -ENOSYS;
>
> spin_lock_irqsave(&tdc->vc.lock, flags);
>
> val = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSRE);
> val &= ~TEGRA_GPCDMA_CHAN_CSRE_PAUSE;
> tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSRE, val);
>
> spin_unlock_irqrestore(&tdc->vc.lock, flags);
>
> return 0;
> }

The reason I separated out register writes was to conveniently call those
in dma_start() and terminate_all(). Do you see any issue there?
The recommended way of terminating a transfer in between is to pause
it before disabling the channel.

dma_desc could be NULL while these functions are called. pause() or
resume() is unneeded if there isn't any transfer going on. Moreover,
if we are to calculate the xfer_size, the check would be mandatory.

Agree with the other comments.

Thanks,
Akhil