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

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Date:   Sun, 30 Jan 2022 13:33:51 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Akhil R <akhilrajeev@...dia.com>, devicetree@...r.kernel.org,
        dmaengine@...r.kernel.org, jonathanh@...dia.com,
        kyarlagadda@...dia.com, ldewangan@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        p.zabel@...gutronix.de, rgumasta@...dia.com, robh+dt@...nel.org,
        thierry.reding@...il.com, vkoul@...nel.org
Cc:     Pavan Kunapuli <pkunapuli@...dia.com>
Subject: Re: [PATCH v17 2/4] dmaengine: tegra: Add tegra gpcdma driver

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;
}