linux-kernel - Re: [PATCH v18 2/4] dmaengine: tegra: Add tegra gpcdma driver

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Date:   Wed, 2 Feb 2022 18:45:09 +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 v18 2/4] dmaengine: tegra: Add tegra gpcdma driver

....
> +static int tegra_dma_pause(struct tegra_dma_channel *tdc)
> +{
> +	int ret;
> +	u32 val;
> +
> +	val = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSRE);
> +	val |= TEGRA_GPCDMA_CHAN_CSRE_PAUSE;
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSRE, val);
> +
> +	/* Wait until busy bit is de-asserted */
> +	ret = readl_relaxed_poll_timeout_atomic(tdc->tdma->base_addr +
> +			tdc->chan_base_offset + TEGRA_GPCDMA_CHAN_STATUS,
> +			val,
> +			!(val & TEGRA_GPCDMA_STATUS_BUSY),
> +			TEGRA_GPCDMA_BURST_COMPLETE_TIME,
> +			TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT);
> +
> +	return ret;
> +}
> +
> +static int tegra_dma_device_pause(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	if (!tdc->tdma->chip_data->hw_support_pause)
> +		return -ENOSYS;
> +
> +	spin_lock_irqsave(&tdc->vc.lock, flags);
> +	ret = tegra_dma_pause(tdc);
> +	if (ret)
> +		dev_err(tdc2dev(tdc), "DMA pause timed out\n");

Why error message shouldn't be printed by tegra_dma_terminate_all()?

The error message should be placed inside of tegra_dma_pause().

...
> +static int tegra_dma_stop_client(struct tegra_dma_channel *tdc)
> +{
> +	int ret;
> +	unsigned long status;
> +	u32 csr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSR);
> +
> +	/*
> +	 * Change the client associated with the DMA channel
> +	 * to stop DMA engine from starting any more bursts for
> +	 * the given client and wait for in flight bursts to complete
> +	 */
> +	csr &= ~(TEGRA_GPCDMA_CSR_REQ_SEL_MASK);
> +	csr |= TEGRA_GPCDMA_CSR_REQ_SEL_UNUSED;
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR, csr);
> +
> +	/* Wait for in flight data transfer to finish */
> +	udelay(TEGRA_GPCDMA_BURST_COMPLETE_TIME);
> +
> +	/* If TX/RX path is still active wait till it becomes
> +	 * inactive
> +	 */
> +
> +	ret = readl_relaxed_poll_timeout_atomic(tdc->tdma->base_addr +
> +				tdc->chan_base_offset +
> +				TEGRA_GPCDMA_CHAN_STATUS,
> +				status,
> +				!(status & (TEGRA_GPCDMA_STATUS_CHANNEL_TX |
> +				TEGRA_GPCDMA_STATUS_CHANNEL_RX)),
> +				5,
> +				TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT);
> +	if (ret) {
> +		dev_err(tdc2dev(tdc), "Timeout waiting for DMA burst completion!\n");
> +		tegra_dma_dump_chan_regs(tdc);
> +	}
> +
> +	return ret;
> +}
> +
> +static int tegra_dma_terminate_all(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long flags;
> +	LIST_HEAD(head);
> +	int err;
> +
> +	spin_lock_irqsave(&tdc->vc.lock, flags);
> +
> +	if (tdc->dma_desc) {
> +		err = tdc->tdma->chip_data->hw_support_pause ?
> +		      tegra_dma_pause(tdc) :
> +		      tegra_dma_stop_client(tdc);

The canonical coding style is:

if (tdc->tdma->chip_data->hw_support_pause)
	err = tegra_dma_pause(tdc);
else
	err = tegra_dma_stop_client(tdc);


But why do you need to pause at all here and can't use
tegra_dma_stop_client() even if pause is supported?