[PATCH v7 0/5] AT91: replace broken TWI driver i2c-at91.c
rmallon at gmail.com
Thu Nov 24 17:13:02 EST 2011
On 24/11/11 17:33, Voss, Nikolaus wrote:
> 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
> 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.
I can confirm this. I worked on a number of AT91 based platforms with
several different i2c client devices and we always had to use the
i2c-gpio driver because the at91-i2c driver would not reliably work with
our client devices.
None of the at91 defconfigs select I2C_AT91, so it should be fairly safe
to remove the old driver. Getting this driver into linux-next (if it
isn't already) would be good so we can see if it does cause problems for
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