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

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Message-ID: <DM5PR12MB18505C4CB4A34F96E74BF28FC0259@DM5PR12MB1850.namprd12.prod.outlook.com>
Date:   Mon, 31 Jan 2022 15:38:07 +0000
From:   Akhil R <akhilrajeev@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>
CC:     "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>,
        Pavan Kunapuli <pkunapuli@...dia.com>
Subject: RE: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

> 31.01.2022 12:09, Akhil R пишет:
> >> В Mon, 31 Jan 2022 04:25:14 +0000
> >> Akhil R <akhilrajeev@...dia.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.

Does the below method look good? bytes_xfer is updated on every ISR and in
tx_status(), the wcount is read to calculate the intermittent value. If the transfer
get complete in between, use wcount as 0 to add sg_req.len to bytes_xfer

static int tegra_dma_get_residual(struct tegra_dma_channel *tdc)
{
	unsigned long wcount = 0, status;
	unsigned int bytes_xfer, residual;
	struct tegra_dma_desc *dma_desc = tdc->dma_desc;
	struct tegra_dma_sg_req *sg_req = dma_desc->sg_req;

	/*
	 * Do not read from CHAN_XFER_COUNT if EOC bit is set
	 * as the transfer would have already completed and
	 * the register could have updated for next transfer
	 * in case of cyclic transfers.
	 */
	status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
	if (!(status & TEGRA_GPCDMA_STATUS_ISE_EOC))
		wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);

	bytes_xfer = dma_desc->bytes_xfer +
		     sg_req[dma_desc->sg_idx - 1].len - (wcount * 4);

	residual = dma_desc->bytes_req - (bytes_xfer % dma_desc->bytes_req);

	return residual;
}

static enum dma_status tegra_dma_tx_status( )
{
	....

	spin_lock_irqsave(&tdc->vc.lock, flags);
	...
	} else if (tdc->dma_desc && tdc->dma_desc->vd.tx.cookie == cookie) {
		residual =  tegra_dma_get_residual(tdc);
		dma_set_residue(txstate, residual);
	} else {
		dev_err(tdc2dev(tdc), "cookie %d is not found\n", cookie);
	}
	spin_unlock_irqrestore(&tdc->vc.lock, flags);

	return ret;
}