linux-kernel - Re: [PATCH v4] i2c: add driver for Rockchip RK3xxx SoC I2C adapter

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Date:	Tue, 10 Jun 2014 10:19:50 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Max Schwarz <max.schwarz@...ine.de>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Heiko Stübner <heiko@...ech.de>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH v4] i2c: add driver for Rockchip RK3xxx SoC I2C adapter


> > > +	/* Synchronization & notification */
> > > +	spinlock_t lock;
> > 
> > Why the lock? The core has per-adapter locks anyhow.
> 
> I'm using it to lock the rk3x_i2c struct during interrupts. It's needed there 
> because an operation can timeout, which means the interrupt can occur at any 
> time and possibly conflict with the cleanup I do after a timeout.
> 
> I looked around in i2c-exynos5.c, i2c-pxa.c and others, and they do it the 
> same way. Could you explain in more detail why it's not needed?

I saw that you disable IRQs on timeout, so that shouldn't happen? You
don't disable IRQs after a successful transfer, though, AFAICS.

> > It looks to me that you STOP after every message? You should use
> > REPEATED_START inbetween messages and only stop after the last message
> > of a transfer.
> 
> I had a fight with the hw today and finally got it to issue a REPEATED_START 
> for multiple "boring" messages. Will be included in the next version.

Great.

> Actually, I wasn't aware that (len == 0) is a valid case. The hw supports it 
> in both modes, I just tested that. So the check is going away.

Also good!


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