linux-kernel - Re: [PATCH 2/2] spi: sprd: Add SPI driver for Spreadtrum SC9860

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Date:   Tue, 7 Aug 2018 15:24:08 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Baolin Wang <baolin.wang@...aro.org>
Cc:     robh+dt@...nel.org, mark.rutland@....com, orsonzhai@...il.com,
        zhang.lyra@...il.com, lanqing.liu@...eadtrum.com,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] spi: sprd: Add SPI driver for Spreadtrum SC9860

On Tue, Aug 07, 2018 at 06:43:38PM +0800, Baolin Wang wrote:
> From: Lanqing Liu <lanqing.liu@...eadtrum.com>
> 
> This patch adds the SPI controller driver for Spreadtrum SC9860 platform.

This all looks pretty clean, a few comments below but nothing too major:

> +static void sprd_spi_chipselect(struct spi_device *sdev, bool cs)
> +{
> +	struct spi_controller *sctlr = sdev->controller;
> +	struct sprd_spi *ss = spi_controller_get_devdata(sctlr);
> +	u32 val;
> +	int ret;
> +
> +	ret = pm_runtime_get_sync(ss->dev);
> +	if (ret < 0) {
> +		dev_err(ss->dev, "failed to resume SPI controller\n");
> +		return;
> +	}

Something else further up the stack should probably have runtime PM
enabled already - we should only be changing chip select as part of a
bigger operation.  If you use the core auto_runtime_pm feature this will
definitely happen.

> +	bits_per_word = bits_per_word > 16 ? round_up(bits_per_word, 16) :
> +		round_up(bits_per_word, 8);

Please

> +	switch (bits_per_word) {
> +	case 8:
> +	case 16:
> +	case 32:

It'd be nice to have a default case, the core should check for you but
it's nice to have defensive programming here.

> +static int sprd_spi_transfer_one(struct spi_controller *sctlr,
> +				 struct spi_device *sdev,
> +				 struct spi_transfer *t)
> +{
> +	struct sprd_spi *ss = spi_controller_get_devdata(sctlr);
> +	int ret;
> +
> +	ret = pm_runtime_get_sync(ss->dev);
> +	if (ret < 0) {
> +		dev_err(ss->dev, "failed to resume SPI controller\n");
> +		goto rpm_err;
> +	}

Same thing with runtime PM here - the core can do this for you.

> +static int sprd_spi_setup(struct spi_device *spi_dev)
> +{
> +	struct spi_controller *sctlr = spi_dev->controller;
> +	struct sprd_spi *ss = spi_controller_get_devdata(sctlr);
> +	int ret;
> +
> +	ret = pm_runtime_get_sync(ss->dev);
> +	if (ret < 0) {
> +		dev_err(ss->dev, "failed to resume SPI controller\n");
> +		return ret;
> +	}
> +
> +	ss->hw_mode = spi_dev->mode;
> +	sprd_spi_init_hw(ss);

This can be called for one chip select while another is in progress so
it's not good to actually configure the hardware here unless the
configuration is in a chip select specific set of registers.  Instead
you should defer to when the transfer is being set up.

> +static int sprd_spi_clk_init(struct platform_device *pdev, struct sprd_spi *ss)
> +{
> +	struct clk *clk_spi, *clk_parent;
> +
> +	clk_spi = devm_clk_get(&pdev->dev, "spi");
> +	if (IS_ERR(clk_spi)) {
> +		dev_warn(&pdev->dev, "can't get the spi clock\n");
> +		clk_spi = NULL;
> +	}

I suspect some of these clocks are essential and you should probably
return an error if you can't get them (especially if probe deferral
becomes a factor).

> +	if (!clk_set_parent(clk_spi, clk_parent))
> +		ss->src_clk = clk_get_rate(clk_spi);
> +	else
> +		ss->src_clk = SPRD_SPI_DEFAULT_SOURCE;

Are upstream DTs going to be missing the clock setup needed here?

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