linux-kernel - Re: [PATCH v2] sdio: optimized SDIO IRQ handling for single irq

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Date:	Wed, 4 May 2011 13:34:21 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Per Forlin <per.forlin@...aro.org>
cc:	linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	Stefan Nilsson XK <stefan.xk.nilsson@...ricsson.com>
Subject: Re: [PATCH v2] sdio: optimized SDIO IRQ handling for single irq

On Wed, 4 May 2011, Per Forlin wrote:

> From: Stefan Nilsson XK <stefan.xk.nilsson@...ricsson.com>
> 
> If there is only 1 function registered it is possible to
> improve performance by directly calling the irq handler
> and avoiding the overhead of reading the CCCR registers.
> 
> Signed-off-by: Per Forlin <per.forlin@...aro.org>
> Acked-by: Ulf Hansson <ulf.hansson@...ricsson.com>
> ---
>  drivers/mmc/core/sdio_irq.c |   30 ++++++++++++++++++++++++++++++
>  include/linux/mmc/card.h    |    1 +
>  2 files changed, 31 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/mmc/core/sdio_irq.c b/drivers/mmc/core/sdio_irq.c
> index b300161..64c4409 100644
> --- a/drivers/mmc/core/sdio_irq.c
> +++ b/drivers/mmc/core/sdio_irq.c
> @@ -32,6 +32,16 @@ static int process_sdio_pending_irqs(struct mmc_card *card)
>  	int i, ret, count;
>  	unsigned char pending;
>  
> +	/*
> +	 * Optimization, if there is only 1 function registered
> +	 * call irq handler directly
> +	 */
> +	if (card->sdio_single_irq && card->sdio_single_irq->irq_handler) {
> +		struct sdio_func *func = card->sdio_single_irq;
> +		func->irq_handler(func);

I think there is little point using a func variable here, especially 
since you already reference the handler pointer in the if() statement.  
Hence:

	if (card->sdio_single_irq && card->sdio_single_irq->irq_handler) {
		card->sdio_single_irq->irq_handler();
		return 1;
	}

> @@ -186,6 +196,24 @@ static int sdio_card_irq_put(struct mmc_card *card)
>  	return 0;
>  }
>  
> +/* If there is only 1 function registered set sdio_single_irq */
> +static void sdio_single_irq_set(struct mmc_card *card)
> +{

The comment is slightly wrong.  This should say "only 1 function 
interrupt registered..."  Nothing prevents this from working with 
multiple functions if only one of them has claimed an interrupt. 

Other than that:

Reviewed-by: Nicolas Pitre <nicolas.pitre@...aro.org>


Nicolas
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