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

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Date:   Mon, 31 Jan 2022 04:25:14 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Yarlagadda <kyarlagadda@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        Rajesh Gumasta <rgumasta@...dia.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>
CC:     Pavan Kunapuli <pkunapuli@...dia.com>
Subject: RE: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

> 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?

Thanks,
Akhil