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Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated one

From Sascha Hauer <s.hauer@pengutronix.de>
Newsgroups linux.kernel
Subject Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated one
Date 2015-11-05 09:50 +0100
Message-ID <qrop3-4fa-7@gated-at.bofh.it> (permalink)
References <qq27f-166-1@gated-at.bofh.it> <qq27g-166-15@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Sun, Nov 01, 2015 at 03:41:36PM +0100, Anton Bondarenko wrote:
> From: Anton Bondarenko <anton_bondarenko@mentor.com>
> 
> Fixed timeout value can fire while transaction is ongoing. This may happen
> because there are no strict requirements on SPI transaction duration.
> Dynamic timeout value is generated based on SCLK and transaction size.
> 
> There is also 4 * SCLK delay between TX bursts related to CS change.
> 
> Signed-off-by: Anton Bondarenko <anton_bondarenko@mentor.com>
> ---
>  drivers/spi/spi-imx.c | 49 +++++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 41 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index bd7b721..9b80c7f 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -57,7 +57,6 @@
>  
>  /* The maximum  bytes that a sdma BD can transfer.*/
>  #define MAX_SDMA_BD_BYTES  (1 << 15)
> -#define IMX_DMA_TIMEOUT (msecs_to_jiffies(3000))
>  struct spi_imx_config {
>  	unsigned int speed_hz;
>  	unsigned int bpw;
> @@ -93,6 +92,7 @@ struct spi_imx_data {
>  	struct clk *clk_per;
>  	struct clk *clk_ipg;
>  	unsigned long spi_clk;
> +	unsigned int spi_bus_clk;
>  
>  	unsigned int count;
>  	void (*tx)(struct spi_imx_data *);
> @@ -314,8 +314,7 @@ static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
>  {
>  	u32 ctrl = MX51_ECSPI_CTRL_ENABLE, dma = 0;
>  	u32 cfg = readl(spi_imx->base + MX51_ECSPI_CONFIG);
> -
> -	u32 clk = config->speed_hz, delay;
> +	u32 delay;
>  
>  	/*
>  	 * The hardware seems to have a race condition when changing modes. The
> @@ -327,7 +326,9 @@ static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
>  	ctrl |= MX51_ECSPI_CTRL_MODE_MASK;
>  
>  	/* set clock speed */
> -	ctrl |= mx51_ecspi_clkdiv(spi_imx->spi_clk, config->speed_hz, &clk);
> +	spi_imx->spi_bus_clk = config->speed_hz;
> +	ctrl |= mx51_ecspi_clkdiv(spi_imx->spi_clk, config->speed_hz,
> +				  &spi_imx->spi_bus_clk);
>  
>  	/* set chip select to use */
>  	ctrl |= MX51_ECSPI_CTRL_CS(config->cs);
> @@ -367,7 +368,7 @@ static int __maybe_unused mx51_ecspi_config(struct spi_imx_data *spi_imx,
>  	 * the SPI communication as the device on the other end would consider
>  	 * the change of SCLK polarity as a clock tick already.
>  	 */
> -	delay = (2 * 1000000) / clk;
> +	delay = (2 * USEC_PER_SEC) / spi_imx->spi_bus_clk;
>  	if (likely(delay < 10))	/* SCLK is faster than 100 kHz */
>  		udelay(delay);
>  	else			/* SCLK is _very_ slow */
> @@ -890,12 +891,40 @@ static void spi_imx_dma_tx_callback(void *cookie)
>  	complete(&spi_imx->dma_tx_completion);
>  }
>  
> +static int spi_imx_calculate_timeout(struct spi_imx_data *spi_imx, int size)
> +{
> +	unsigned long coef1 = 1;
> +	unsigned long coef2 = MSEC_PER_SEC;
> +	unsigned long timeout = 0;
> +
> +	/* Swap coeficients to avoid div by 0 */
> +	if (spi_imx->spi_bus_clk < MSEC_PER_SEC) {
> +		coef1 = MSEC_PER_SEC;
> +		coef2 = 1;
> +	}
> +
> +	/* Time with actual data transfer */
> +	timeout += DIV_ROUND_UP(8 * size * coef1,
> +				spi_imx->spi_bus_clk / coef2);
> +
> +	/* Take CS change delay related to HW */
> +	timeout += DIV_ROUND_UP((size - 1) * 4 * coef1,
> +				spi_imx->spi_bus_clk / coef2);
> +
> +	/* Add extra second for scheduler related activities */
> +	timeout += MSEC_PER_SEC;
> +
> +	/* Double calculated timeout */
> +	return msecs_to_jiffies(2 * timeout);
> +}

I think you can simplify this function to:

	timeout = size * 8 / spi_imx->spi_bus_clk;
	timeout += 2;

	return msecs_to_jiffies(timeout * MSEC_PER_SEC);

The rationale is that when size * 8 / spi_imx->spi_bus_clk is 0 then we
can add another second and be fine. No need to calculate this more
accurate, in the end it's important to catch the timeout. If we do this
one or two seconds too late doesn't matter.

Sascha

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Thread

[PATCH v3 0/7] Improvements for SPI IMX driver for Freescale IMX51, IMX53 and IMX6 Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
  [PATCH v3 5/7] spi: imx: Add support for loopback for ECSPI controllers Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 5/7] spi: imx: Add support for loopback for ECSPI  controllers Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
  [PATCH v3 6/7] spi: imx: return error from dma channel request Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 6/7] spi: imx: return error from dma channel request Sascha Hauer <s.hauer@pengutronix.de> - 2015-11-05 10:00 +0100
      Re: [PATCH v3 6/7] spi: imx: return error from dma channel request Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-05 17:10 +0100
        Re: [PATCH v3 6/7] spi: imx: return error from dma channel request Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
        Re: [PATCH v3 6/7] spi: imx: return error from dma channel request Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
  [PATCH v3 4/7] spi: imx: add function to check for IMX51 family controller Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 4/7] spi: imx: add function to check for IMX51 family  controller Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
  [PATCH v3 3/7] spi: imx: add support for all SPI word width for DMA transfer Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
  [PATCH v3 1/7] spi: imx: Fix DMA transfer Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-04 22:10 +0100
    Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer Sascha Hauer <s.hauer@pengutronix.de> - 2015-11-05 09:40 +0100
      Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-05 18:00 +0100
        Re: [PATCH v3 1/7] spi: imx: Fix DMA transfer Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
  [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine is pending Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine  is pending Sascha Hauer <s.hauer@pengutronix.de> - 2015-11-05 10:00 +0100
      Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine  is pending Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-05 17:20 +0100
        Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine  is pending Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100
  [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated one Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-01 15:50 +0100
    Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated  one Sascha Hauer <s.hauer@pengutronix.de> - 2015-11-05 09:50 +0100
      Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated  one Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-10 21:30 +0100
        Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated  one Sascha Hauer <s.hauer@pengutronix.de> - 2015-11-11 09:20 +0100
          Re: [PATCH v3 2/7] spi: imx: replace fixed timeout with calculated  one Anton Bondarenko <anton.bondarenko.sama@gmail.com> - 2015-11-14 11:10 +0100

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