linux-kernel - Re: [Patch v2 2/4] dmaengine: tegra: Add Tegra GPC DMA driver

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Message-ID: <bc7d0d9d-ac7f-b720-64f5-63e0c76e6786@gmail.com>
Date:   Thu, 6 Aug 2020 16:46:14 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Rajesh Gumasta <rgumasta@...dia.com>, ldewangan@...dia.com,
        jonathanh@...dia.com, vkoul@...nel.org, dan.j.williams@...el.com,
        thierry.reding@...il.com, p.zabel@...gutronix.de,
        dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     kyarlagadda@...dia.com, Pavan Kunapuli <pkunapuli@...dia.com>
Subject: Re: [Patch v2 2/4] dmaengine: tegra: Add Tegra GPC DMA driver

06.08.2020 10:30, Rajesh Gumasta пишет:
...
> +/*
> + * Save and restore csr and channel register on pm_suspend
> + * and pm_resume respectively
> + */
> +static int __maybe_unused tegra_dma_pm_suspend(struct device *dev)
> +{
> +	struct tegra_dma *tdma = dev_get_drvdata(dev);
> +	int i;
> +
> +	for (i = 0; i < tdma->chip_data->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +		struct tegra_dma_channel_regs *ch_reg = &tdc->channel_reg;
> +
> +		ch_reg->csr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSR);
> +		ch_reg->src_ptr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_SRC_PTR);
> +		ch_reg->dst_ptr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_DST_PTR);
> +		ch_reg->high_addr_ptr = tdc_read(tdc,
> +						 TEGRA_GPCDMA_CHAN_HIGH_ADDR_PTR);
> +		ch_reg->mc_seq = tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ);
> +		ch_reg->mmio_seq = tdc_read(tdc, TEGRA_GPCDMA_CHAN_MMIOSEQ);
> +		ch_reg->wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_WCOUNT);
> +	}
> +	return 0;
> +}
> +
> +static int __maybe_unused tegra_dma_pm_resume(struct device *dev)
> +{
> +	struct tegra_dma *tdma = dev_get_drvdata(dev);
> +	int i;
> +
> +	for (i = 0; i < tdma->chip_data->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +		struct tegra_dma_channel_regs *ch_reg = &tdc->channel_reg;
> +
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_WCOUNT, ch_reg->wcount);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_DST_PTR, ch_reg->dst_ptr);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_SRC_PTR, ch_reg->src_ptr);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_HIGH_ADDR_PTR,
> +			  ch_reg->high_addr_ptr);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_MMIOSEQ, ch_reg->mmio_seq);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_MCSEQ, ch_reg->mc_seq);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR,
> +			  (ch_reg->csr & ~TEGRA_GPCDMA_CSR_ENB));
> +	}
> +	return 0;
> +}
> +
> +static const struct __maybe_unused dev_pm_ops tegra_dma_dev_pm_ops = {
> +	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(tegra_dma_pm_suspend, tegra_dma_pm_resume)
> +};

Please explain why this is needed. All DMA should be stopped (not
paused) on system's suspend, shouldn't it?