[PATCH] i2c: Bus drivers don't have to support I2C_M_REV_DIR_ADDR

[PATCH] i2c: Bus drivers don't have to support I2C_M_REV_DIR_ADDR

[Jean Delvare]

I2C bus drivers don't have to support I2C_M_REV_DIR_ADDR. It is a
deviation from the I2C specification, which only makes sense to
implement when really needed.

Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
Cc: Ben Dooks <ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>
---
 drivers/i2c/busses/i2c-iop3xx.c   |    6 ------
 drivers/i2c/busses/i2c-mv64xxx.c  |    3 ---
 drivers/i2c/busses/i2c-powermac.c |    2 --
 3 files changed, 11 deletions(-)

--- linux-2.6.32-rc1.orig/drivers/i2c/busses/i2c-iop3xx.c	2009-06-10 05:05:27.000000000 +0200
+++ linux-2.6.32-rc1/drivers/i2c/busses/i2c-iop3xx.c	2009-09-30 21:34:01.000000000 +0200
@@ -56,12 +56,6 @@ iic_cook_addr(struct i2c_msg *msg)
 	if (msg->flags & I2C_M_RD)
 		addr |= 1;
 
-	/*
-	 * Read or Write?
-	 */
-	if (msg->flags & I2C_M_REV_DIR_ADDR)
-		addr ^= 1;
-
 	return addr;   
 }
 
--- linux-2.6.32-rc1.orig/drivers/i2c/busses/i2c-mv64xxx.c	2009-09-28 10:28:36.000000000 +0200
+++ linux-2.6.32-rc1/drivers/i2c/busses/i2c-mv64xxx.c	2009-09-30 21:33:45.000000000 +0200
@@ -338,9 +338,6 @@ mv64xxx_i2c_prepare_for_io(struct mv64xx
 	if (msg->flags & I2C_M_RD)
 		dir = 1;
 
-	if (msg->flags & I2C_M_REV_DIR_ADDR)
-		dir ^= 1;
-
 	if (msg->flags & I2C_M_TEN) {
 		drv_data->addr1 = 0xf0 | (((u32)msg->addr & 0x300) >> 7) | dir;
 		drv_data->addr2 = (u32)msg->addr & 0xff;
--- linux-2.6.32-rc1.orig/drivers/i2c/busses/i2c-powermac.c	2009-09-30 20:29:42.000000000 +0200
+++ linux-2.6.32-rc1/drivers/i2c/busses/i2c-powermac.c	2009-09-30 21:33:39.000000000 +0200
@@ -156,8 +156,6 @@ static int i2c_powermac_master_xfer(	str
 		return -EINVAL;
 	read = (msgs->flags & I2C_M_RD) != 0;
 	addrdir = (msgs->addr << 1) | read;
-	if (msgs->flags & I2C_M_REV_DIR_ADDR)
-		addrdir ^= 1;
 
 	rc = pmac_i2c_open(bus, 0);
 	if (rc)


-- 
Jean Delvare

Re: [PATCH] i2c: Bus drivers don't have to support I2C_M_REV_DIR_ADDR

[Ben Dooks]

On Wed, Sep 30, 2009 at 10:22:44PM +0200, Jean Delvare wrote:
> I2C bus drivers don't have to support I2C_M_REV_DIR_ADDR. It is a
> deviation from the I2C specification, which only makes sense to
> implement when really needed.

Probably the right thing to do, does anything actually use this
support?
 
> Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
> Cc: Ben Dooks <ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>
> ---
>  drivers/i2c/busses/i2c-iop3xx.c   |    6 ------
>  drivers/i2c/busses/i2c-mv64xxx.c  |    3 ---
>  drivers/i2c/busses/i2c-powermac.c |    2 --

I assume that I should merge this in my -next tree?

-- 
Ben (ben-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'

Re: [PATCH] i2c: Bus drivers don't have to support I2C_M_REV_DIR_ADDR

[Jean Delvare]

Hi Ben,

On Tue, 13 Oct 2009 23:50:10 +0100, Ben Dooks wrote:
> On Wed, Sep 30, 2009 at 10:22:44PM +0200, Jean Delvare wrote:
> > I2C bus drivers don't have to support I2C_M_REV_DIR_ADDR. It is a
> > deviation from the I2C specification, which only makes sense to
> > implement when really needed.
> 
> Probably the right thing to do, does anything actually use this
> support?

As far as I know, the only chip which uses this is the "Maven" which is
found on some Matrox G450 graphics cards to handle the second head.

As the i2c-matroxfb driver builds on top of i2c-algo-bit, i2c-algo-bit
is the only driver which needs to implement I2C_M_REV_DIR_ADDR.

I've left it in i2c-algo-pcf and i2c-s3c2410 for now because at least
they properly declare the I2C_FUNC_PROTOCOL_MANGLING functionality, but
this could be reconsidered.

The other protocol mangling flags are in a similar situation. For
example I2C_M_NOSTART is only used by the Intel i915 and Matrox Maven
chips. Both use i2c-algo-but, but no less than 9 other I2C adapter
drivers implement it! Most of these implementations have most probably
never been tested, and I wouldn't be surprised if some don't work.

I2C_M_IGNORE_NAK is only used by the msp3400 audio processing driver.
But it is implemented by embedded I2C adapter drivers which probably
will never see this chip: i2c-davinci, i2c-omap, i2c-s3c2410 and
i2c-stu300.

I2C_M_NO_RD_ACK is only used by the ks0127 video driver, and only
i2c-algo-bit implements it. That one is correct.


> > Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
> > Cc: Ben Dooks <ben-linux-elnMNo+KYs3YtjvyW6yDsg@public.gmane.org>
> > ---
> >  drivers/i2c/busses/i2c-iop3xx.c   |    6 ------
> >  drivers/i2c/busses/i2c-mv64xxx.c  |    3 ---
> >  drivers/i2c/busses/i2c-powermac.c |    2 --
> 
> I assume that I should merge this in my -next tree?

Probably, yes. For now I have this patch in my own -next tree, but as
all drivers affected are embedded ones, it would fit better in yours.

I leave it up to you to decide what to do with the i2c-s3c2410 driver.
As I understand it, it doesn't need to implement I2C_M_REV_DIR_ADDR nor
I2C_M_IGNORE_NAK nor I2C_M_NOSTART, so you could simplify the code a
bit and stop defining I2C_FUNC_PROTOCOL_MANGLING.

BTW, is your -next tree visible somewhere? It might be convenient for
me to be able to check what it includes.

-- 
Jean Delvare