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

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Date:	Wed, 4 May 2011 18:23:38 +0200
From:	Michał Mirosław <mirqus@...il.com>
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,
	Chris Ball <cjb@...top.org>,
	Stefan Nilsson XK <stefan.xk.nilsson@...ricsson.com>
Subject: Re: [PATCH v2] sdio: optimized SDIO IRQ handling for single irq

2011/5/4 Per Forlin <per.forlin@...aro.org>:
> 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.
>
[...]
> --- 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);
> +               return 1;
> +       }
[...]

The second condition can be avoided:

in process_sdio_pending_irqs():

if (card->sdio_irq_func)
   call handler and return

in sdio_claim_irq():

  card->func->irq_handler = ...
  if (host->sdio_irqs == 1)
    card->sdio_irq_func = func;
  else
    card->sdio_irq_func = NULL;

in sdio_release_irq():

  card->sdio_irq_func = NULL;
  card->func->irq_handler = ...
  sdio_card_irq_put();
  if (host->sdio_irqs == 1)
    sdio_single_irq_set(func->card);

in struct mmc_card:
  struct sdio_func        *sdio_irq_func;

Best Regards,
Michał Mirosław
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