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

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Date:	Wed, 4 May 2011 21:48:12 +0200
From:	Per Forlin <per.forlin@...aro.org>
To:	Nicolas Pitre <nicolas.pitre@...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 4 May 2011 19:34, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> 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;
>        }
>
What do you think about:
+       struct sdio_func *func = card->sdio_single_irq;
+
+       /*
+        * Optimization, if there is only 1 function interrupt registered
+        * call irq handler directly
+        */
+       if (func) {
+               func->irq_handler(func);
+               return 1;
+       }

-                       struct sdio_func *func = card->sdio_func[i - 1];
+                       func = card->sdio_func[i - 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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