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

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Date:	Wed, 4 May 2011 19:00:10 +0200
From:	Per Forlin <per.forlin@...aro.org>
To:	Michał Mirosław <mirqus@...il.com>
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 Michał Mirosław <mirqus@...il.com>:
> 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
>
I added the second condition as a sanity check. Same check is used in
the main for loop
>	ret = -EINVAL;
>			} else if (func->irq_handler) {
>				func->irq_handler(func);
Is the second check necessary here?

> in sdio_claim_irq():
>
>  card->func->irq_handler = ...
>  if (host->sdio_irqs == 1)
>    card->sdio_irq_func = func;
>  else
>    card->sdio_irq_func = NULL;
I wanted to keep it simple and use same function in claim and release.
Your code looks nice.
Is if safe to not check the condition "(card->host->caps &
MMC_CAP_SDIO_IRQ)". What happens if the SDIO is in polling mode?

>
> 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);
This works for me.

>
> in struct mmc_card:
>  struct sdio_func        *sdio_irq_func;
The name sdio_single_irq indicates it is only used for single irq.
"sdio_irq_func" is too generic I think. But the your name is shorter
and makes the indentation look nicer.
Not a big deal really.

I will wait until tomorrow to post patch v3. This will give time for
other to comment as well.

> Best Regards,
> Michał Mirosław
>
Thanks for your feedback,
Per
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