linux-kernel - Re: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip

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Message-ID: <20110318151219.7aedc765@lxorguk.ukuu.org.uk>
Date:	Fri, 18 Mar 2011 15:12:19 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	<Waldemar.Rymarkiewicz@...to.com>
Cc:	<linux-i2c@...r.kernel.org>, <arnd@...db.de>,
	<sameo@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<hthebaud@...idefr.com>, <matti.j.aaltonen@...ia.com>
Subject: Re: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip

> >Would it not be lighter to use atomic bit ops ?
> 
> Do you mean  in order to remove rx_mutex? 
> 
> mutex_lock(&info->rx_mutex);
> atomic_set(info->irq_state ,1);
> mutex_unlock(&info->rx_mutex);
> 
> looks a bit strange. I still need the rx_mutex to protect irq_state while reading i2c.
> 
> 	mutex_lock(&info->rx_mutex);
> 	ret = i2c_master_recv(client, info->buf, info->buflen);
> 	info->irq_state = 0;
> 	mutex_unlock(&info->rx_mutex);
> 

I was thinking clear_bit/test_and_set_bit rather than atomic_t operations.

ie in the IRQ

	clear_bit(0, &info->irq_state);


in the main path

	if (test_and_set_bit(0, &info->state))
		i2c_master_recv(...)

but if the mutex is needed anyway it doesn't help make the code saner.
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