linux-kernel - Re: [PATCH 2/2] spi: meson-spicc: Use pinctrl to drive CLK line when idle

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Date:   Wed, 10 Aug 2022 10:52:16 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Amjad Ouled-Ameur <aouledameur@...libre.com>, broonie@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org,
        narmstrong@...libre.com, Da Xue <da@...re.computer>
Subject: Re: [PATCH 2/2] spi: meson-spicc: Use pinctrl to drive CLK line
 when idle


On Tue 09 Aug 2022 at 19:20, Amjad Ouled-Ameur <aouledameur@...libre.com> wrote:

> Between SPI transactions, all SPI pins are in HiZ state. When using the SS
> signal from the SPICC controller it's not an issue because when the
> transaction resumes all pins come back to the right state at the same time
> as SS.
>
> The problem is when we use CS as a GPIO. In fact, between the GPIO CS
> state change and SPI pins state change from idle, you can have a missing or
> spurious clock transition.
>
> Set a bias on the clock depending on the clock polarity requested before CS
> goes active, by passing a special "idle-low" and "idle-high" pinctrl state
> and setting the right state at a start of a message
>
> Reported-by: Da Xue <da@...re.computer>
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> Signed-off-by: Amjad Ouled-Ameur <aouledameur@...libre.com>
> ---
>  arch/arm64/boot/dts/amlogic/meson-gxl.dtsi | 14 ++++++++
>  drivers/spi/spi-meson-spicc.c              | 39 +++++++++++++++++++++-

These 2 changes should not be in the same patch.

>  2 files changed, 52 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> index c3ac531c4f84..04e9d0f1bde0 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi

Does the problem applies only the gxl ? not gxbb, g12, axg ?

> @@ -429,6 +429,20 @@ mux {
>  			};
>  		};
>  
> +		spi_idle_high_pins: spi-idle-high-pins {
> +			mux {
> +				groups = "spi_sclk";
> +				bias-pull-up;
> +			};
> +		};
> +
> +		spi_idle_low_pins: spi-idle-low-pins {
> +			mux {
> +				groups = "spi_sclk";
> +				bias-pull-down;

Would it be safer to properly drive the pin in push-pull mode ?
Like using gpio pinumux mode and output-high/output-low pinconf ?

> +			};
> +		};
> +
>  		spi_ss0_pins: spi-ss0 {
>  			mux {
>  				groups = "spi_ss0";
> diff --git a/drivers/spi/spi-meson-spicc.c b/drivers/spi/spi-meson-spicc.c
> index 0bc7daa7afc8..d42171ee1d61 100644
> --- a/drivers/spi/spi-meson-spicc.c
> +++ b/drivers/spi/spi-meson-spicc.c
> @@ -21,6 +21,7 @@
>  #include <linux/types.h>
>  #include <linux/interrupt.h>
>  #include <linux/reset.h>
> +#include <linux/pinctrl/consumer.h>
>  
>  /*
>   * The Meson SPICC controller could support DMA based transfers, but is not
> @@ -166,14 +167,31 @@ struct meson_spicc_device {
>  	unsigned long			tx_remain;
>  	unsigned long			rx_remain;
>  	unsigned long			xfer_remain;
> +	struct pinctrl			*pinctrl;
> +	struct pinctrl_state		*pins_idle_high;
> +	struct pinctrl_state		*pins_idle_low;
>  };
>  
>  static void meson_spicc_oen_enable(struct meson_spicc_device *spicc)
>  {
>  	u32 conf;
>  
> -	if (!spicc->data->has_oen)
> +	if (!spicc->data->has_oen) {
> +		/* Try to get pinctrl states for idle high/low */
> +		spicc->pins_idle_high = pinctrl_lookup_state(spicc->pinctrl,
> +							     "idle-high");
> +		if (IS_ERR(spicc->pins_idle_high)) {
> +			dev_warn(&spicc->pdev->dev, "can't get idle-high pinctrl\n");
> +			spicc->pins_idle_high = NULL;
> +		}
> +		spicc->pins_idle_low = pinctrl_lookup_state(spicc->pinctrl,
> +							     "idle-low");
> +		if (IS_ERR(spicc->pins_idle_low)) {
> +			dev_warn(&spicc->pdev->dev, "can't get idle-low pinctrl\n");
> +			spicc->pins_idle_low = NULL;
> +		}
>  		return;
> +	}
>  
>  	conf = readl_relaxed(spicc->base + SPICC_ENH_CTL0) |
>  		SPICC_ENH_MOSI_OEN | SPICC_ENH_CLK_OEN | SPICC_ENH_CS_OEN;
> @@ -438,6 +456,16 @@ static int meson_spicc_prepare_message(struct spi_master *master,
>  	else
>  		conf &= ~SPICC_POL;
>  
> +	if (!spicc->data->has_oen) {
> +		if (spi->mode & SPI_CPOL) {
> +			if (spicc->pins_idle_high)
> +				pinctrl_select_state(spicc->pinctrl, spicc->pins_idle_high);
> +		} else {
> +			if (spicc->pins_idle_low)
> +				pinctrl_select_state(spicc->pinctrl, spicc->pins_idle_low);
> +		}
> +	}
> +
>  	if (spi->mode & SPI_CPHA)
>  		conf |= SPICC_PHA;
>  	else
> @@ -482,6 +510,9 @@ static int meson_spicc_unprepare_transfer(struct spi_master *master)
>  
>  	device_reset_optional(&spicc->pdev->dev);
>  
> +	if (!spicc->data->has_oen)
> +		pinctrl_select_default_state(&spicc->pdev->dev);
> +
>  	return 0;
>  }
>  
> @@ -733,6 +764,12 @@ static int meson_spicc_probe(struct platform_device *pdev)
>  		goto out_core_clk;
>  	}
>  
> +	spicc->pinctrl = devm_pinctrl_get(&pdev->dev);
> +	if (IS_ERR(spicc->pinctrl)) {
> +		ret = PTR_ERR(spicc->pinctrl);
> +		goto out_clk;
> +	}
> +
>  	device_reset_optional(&pdev->dev);
>  
>  	master->num_chipselect = 4;