linux-kernel - Re: [PATCH] mtd: pxa3xx-nand: handle PIO in threaded interrupt

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Date:	Wed, 18 Feb 2015 11:16:46 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: pxa3xx-nand: handle PIO in threaded interrupt

On Tue, Feb 17, 2015 at 09:06:57PM +0100, Robert Jarzmik wrote:
> Change the handling of the data stage in the driver : don't pump data in
> the top-half interrupt, but rather schedule a thread for non dma cases.
> 
> This will enable latencies in the data pumping, especially if delays are
> required. Moreover platform shall be more reactive as other interrupts
> can be served while pumping data.
> 
> No throughput degradation was observed, at least on the zylonite
> platform, while a slight degradation was being expected.
> 
> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>

Tested-by: Maxime Ripard <maxime.ripard@...e-electrons.com>

On a sidenote...

> ---
>  drivers/mtd/nand/pxa3xx_nand.c | 23 ++++++++++++++++++++---
>  1 file changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/nand/pxa3xx_nand.c b/drivers/mtd/nand/pxa3xx_nand.c
> index 96b0b1d..237c92c 100644
> --- a/drivers/mtd/nand/pxa3xx_nand.c
> +++ b/drivers/mtd/nand/pxa3xx_nand.c
> @@ -569,11 +569,25 @@ static void start_data_dma(struct pxa3xx_nand_info *info)
>  {}
>  #endif
>  
> +static irqreturn_t pxa3xx_nand_irq_thread(int irq, void *data)
> +{
> +	struct pxa3xx_nand_info *info = data;
> +
> +	handle_data_pio(info);
> +
> +	info->state = STATE_CMD_DONE;
> +	nand_writel(info, NDSR, NDSR_WRDREQ | NDSR_RDDREQ);
> +	enable_int(info, NDCR_INT_MASK);
> +
> +	return IRQ_HANDLED;
> +}
> +
>  static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
>  {
>  	struct pxa3xx_nand_info *info = devid;
>  	unsigned int status, is_completed = 0, is_ready = 0;
>  	unsigned int ready, cmd_done;
> +	irqreturn_t ret = IRQ_HANDLED;
>  
>  	if (info->cs == 0) {
>  		ready           = NDSR_FLASH_RDY;
> @@ -613,9 +627,11 @@ static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
>  			start_data_dma(info);
>  			goto NORMAL_IRQ_EXIT;
>  		} else {
> +			disable_int(info, NDCR_INT_MASK);
>  			info->state = (status & NDSR_RDDREQ) ?
>  				      STATE_PIO_READING : STATE_PIO_WRITING;
> -			handle_data_pio(info);
> +			ret = IRQ_WAKE_THREAD;
> +			goto NORMAL_IRQ_EXIT;
>  		}
>  	}
>  	if (status & cmd_done) {
> @@ -656,7 +672,7 @@ static irqreturn_t pxa3xx_nand_irq(int irq, void *devid)
>  	if (is_ready)
>  		complete(&info->dev_ready);
>  NORMAL_IRQ_EXIT:
> -	return IRQ_HANDLED;
> +	return ret;
>  }
>  
>  static inline int is_buf_blank(uint8_t *buf, size_t len)
> @@ -1672,7 +1688,8 @@ static int alloc_nand_resource(struct platform_device *pdev)
>  	/* initialize all interrupts to be disabled */
>  	disable_int(info, NDSR_MASK);
>  
> -	ret = request_irq(irq, pxa3xx_nand_irq, 0, pdev->name, info);
> +	ret = request_threaded_irq(irq, pxa3xx_nand_irq,
> +				   pxa3xx_nand_irq_thread, 0, pdev->name, info);

Using IRQF_ONESHOT would allow you not to do the interrupt enable /
disable dance.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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