[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Peter Korsgaard]

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[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Tolunay Orkun]

Peter,

I believe the implementation was correct but the comment was wrong. It 
should be a write transaction with just address byte. After the address 
byte is transmitted the I2C slave will acknowledge (if present) and we 
finish the transaction by generating the stop condition. i.e. fake write.

Best regards,
Tolunay

Peter Korsgaard wrote:
> Hi,
> 
> The following little patch makes the i2c_probe function use reads
> instead of writes to match the comment (broken in r1.2).
> 
> * Patch by Peter Korsgaard, 26 May 2005:
>   Use reads instead of writes for probe in soft_i2c.
> 
> 
> 
> ------------------------------------------------------------------------
> 
> Index: common/soft_i2c.c
> ===================================================================
> RCS file: /cvsroot/u-boot/u-boot/common/soft_i2c.c,v
> retrieving revision 1.5
> diff -u -p -u -r1.5 soft_i2c.c
> --- common/soft_i2c.c	21 Nov 2004 00:06:35 -0000	1.5
> +++ common/soft_i2c.c	26 May 2005 19:45:05 -0000
> @@ -290,7 +290,7 @@ int i2c_probe(uchar addr)
>  
>  	/* perform 1 byte read transaction */
>  	send_start();
> -	rc = write_byte ((addr << 1) | 0);
> +	rc = write_byte ((addr << 1) | 1);
>  	send_stop();
>  
>  	return (rc ? 1 : 0);
> 
> 
> ------------------------------------------------------------------------
> 
> 

[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Peter Korsgaard]

>>>>> "Tolunay" == Tolunay Orkun <listmember@orkun.us> writes:

Hi, and sorry for the slow response!

 Tolunay> Peter, I believe the implementation was correct but the
 Tolunay> comment was wrong. It should be a write transaction with
 Tolunay> just address byte. After the address byte is transmitted the
 Tolunay> I2C slave will acknowledge (if present) and we finish the
 Tolunay> transaction by generating the stop condition. i.e. fake
 Tolunay> write.

Why write? Wouldn't a zero byte read transaction be safer?

-- 
Bye, Peter Korsgaard

[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Tolunay Orkun]

Peter Korsgaard wrote:

>>>>>>"Tolunay" == Tolunay Orkun <listmember@orkun.us> writes:
>>>>>>            
>>>>>>
>
>Hi, and sorry for the slow response!
>
> Tolunay> Peter, I believe the implementation was correct but the
> Tolunay> comment was wrong. It should be a write transaction with
> Tolunay> just address byte. After the address byte is transmitted the
> Tolunay> I2C slave will acknowledge (if present) and we finish the
> Tolunay> transaction by generating the stop condition. i.e. fake
> Tolunay> write.
>
>Why write? Wouldn't a zero byte read transaction be safer?
>
>  
>
I have read somewhere (that I cannot find now), that some device would 
lock up on 0-byte read vs 0-byte write. Since the current code is 
working as it is unless there is demonstrable problem with it, I would 
fix the comment only.

[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Eugene Surovegin]

On Tue, Jun 14, 2005 at 04:34:38PM -0500, Tolunay Orkun wrote:
> Peter Korsgaard wrote:
> 
> >>>>>>"Tolunay" == Tolunay Orkun <listmember@orkun.us> writes:
> >>>>>>           
> >>>>>>
> >
> >Hi, and sorry for the slow response!
> >
> >Tolunay> Peter, I believe the implementation was correct but the
> >Tolunay> comment was wrong. It should be a write transaction with
> >Tolunay> just address byte. After the address byte is transmitted the
> >Tolunay> I2C slave will acknowledge (if present) and we finish the
> >Tolunay> transaction by generating the stop condition. i.e. fake
> >Tolunay> write.
> >
> >Why write? Wouldn't a zero byte read transaction be safer?
> >
> > 
> >
> I have read somewhere (that I cannot find now), that some device would 
> lock up on 0-byte read vs 0-byte write. Since the current code is 
> working as it is unless there is demonstrable problem with it, I would 
> fix the comment only.

Ebony (PPC440GP eval board) has a device like this, IIRC it's a clock 
driver, zero-read locks the bus completely.

In general, zero write is safer, also SMBUS spec defines such 
transaction as SMBUS QUICK; interestingly, there is no read 
equivalent :).

Also, from personal testing, using zero-write as detection hack, 
yields more devices than zero-read.

-- 
Eugene

[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Peter Korsgaard]

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[U-Boot-Users] [PATCH] soft_i2c/i2c_probe(): Perform reads instead of writes

[Wolfgang Denk]

In message <87ekbt3g7h.fsf@p4.48ers.dk> you wrote:
> 
> * Patch by Peter Korsgaard, 26 May 2005:
>   Use reads instead of writes for probe in soft_i2c.

Rejected. Tolunay's explanation was correct:  only  the  comment  was
wrong. Fixed the comment now.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
I distrust all systematisers, and avoid them. The will  to  a  system
shows a lack of honesty.
- Friedrich Wilhelm Nietzsche _G?tzen-D?mmerung [The Twilight of  the
Idols]_ ``Maxims and Missiles'' no. 26