linux-kernel - RE: [PATCH v7 0/5] AT91: replace broken TWI driver i2c-at91.c

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Date:	Thu, 24 Nov 2011 07:33:09 +0100
From:	"Voss, Nikolaus" <N.Voss@...nmann.de>
To:	"'Ben Dooks'" <ben-i2c@...ff.org>
CC:	"'linux-i2c@...r.kernel.org'" <linux-i2c@...r.kernel.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'ben-linux@...ff.org'" <ben-linux@...ff.org>,
	"'carsten.behling@...z-fricke.com'" <carsten.behling@...z-fricke.com>
Subject: RE: [PATCH v7 0/5] AT91: replace broken TWI driver i2c-at91.c

Hi,

Ben Dooks wrote on 2011-11-24:
> On Wed, Nov 23, 2011 at 04:35:55PM +0100, Nikolaus Voss wrote:
> > The old driver has two main deficencies:
> > i)  No repeated start (Sr) condiction is possible, this makes it unusable
> >     e.g. for most SMBus transfers.
> > ii) I/O was done with polling/busy waiting what caused over-/underruns
> >     even at light system loads and clock speeds.
> >
> > The new driver overcomes these deficencies and in addition allows for
> > more than one TWI interface.
> >
> > A remaining limitation is the fact, that only one repeated start is
> > possible (two concatenated messages). This limitation is imposed by
> > the hardware. However, this should not be a problem as all common
> > i2c-client communication does not rely on more than one repeated start.
> >
> > v7: Patch 4/5: i)  fix bug if internal address > 1 byte
> >                ii) send stop when len == 1
> >                    (both reported by Carsten Behling)
> > v6: Patch 5/5: support for I2C_SMBUS_BLOCK_DATA transfers.
> >     Better use of clk_(un)prepare().
> >     More sensible transfer timeout.
> > v5: Another round of review comments from Ryan Mallon, Felipe Balbi
> >     and Russell King: convert twi clk to use .dev_id, cleanups
> > v4: Integrated more review comments from Ryan Mallon and Felipe Balbi:
> >     Moved register include file to local include, code cleanups
> > v3: Integrated review comments from Ryan Mallon and Felipe Balbi
> > v2: Fixed whitespace issue
> >
> > Nikolaus Voss (5):
> >   drivers/i2c/busses/i2c-at91.c: remove broken driver
> >   Replace clk_lookup.con_id with clk_lookup.dev_id entries for twi clk
> >   drivers/i2c/busses/i2c-at91.c: add new driver
> >   G45 TWI: remove open drain setting for twi function gpios
> >   i2c-at91.c: add SMBUS_READ_BLOCK_DATA functionality
> 
> Is the original driver so broken that the two could not co-exist, or are
> we making so many changes that there's no point in keeping the original
> one?

The old driver was marked as broken for the above reasons and I can hardly
imagine any setup in which it would be preferable to i2c-gpio. So it does
not make any sense to keep the old driver alive. Though inspired by the old
driver, the new one is almost a rewrite from scratch, so for better reviewing,
I removed the old instead of doing a diff.

Niko

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