Re: [PATCH] I2C block read

[Alexander Atanasov <alex@ssi.bg>]

On Wed, 7 Jun 2006 19:49:43 +0200
Jean Delvare wrote:

> Hi Alexander,
> 
> > 	When doing i2c block read the lenght is passed as the first
> > byte of the buffer, so we must copy it from user otherwise temp is
> > uninitialized.
> 
> > --- drivers/i2c/i2c-dev.c.orig	2006-01-04 02:00:00.000000000
> > +0200 +++ drivers/i2c/i2c-dev.c	2006-06-07
> > 19:46:08.000000000 +0300 @@ -337,6 +337,7 @@
> >  
> >  		if ((data_arg.size == I2C_SMBUS_PROC_CALL) || 
> >  		    (data_arg.size == I2C_SMBUS_BLOCK_PROC_CALL)
> > || 
> > +		    (data_arg.size == I2C_SMBUS_BLOCK_DATA) ||
> >  		    (data_arg.read_write == I2C_SMBUS_WRITE)) {
> >  			if (copy_from_user(&temp, data_arg.data,
> > datasize)) return -EFAULT;
> 
> Nack. Firstly, your comment says I2C block read, but your code changes
> SMBus block read. These are two different transactions. Secondly, for
> SMBus block read, the master doesn't ask for a given number of bytes.
> Instead, the chip decides and returns the number of (following) bytes
> as the first byte of the read part of the transaction. Check the SMBus
> specification.
> 
> So your patch is not correct, sorry.


	10x. Here is the case:
I use SMBus block read with scx200_acb as a bus it uses the lenght
which is as i say uninitialized and tries to read a number of random bytes
from the board i use. And it doesn't return the lenght as a first byte,
so the drivers reads until it gets an oops. Which in turn makes me wonder
why with this patch i correcly receive the number of bytes i pass,
looking at the driver i can not see that it gets the lenght from the read data.
I don't know well SMBus/I2C specs but read with buffer and no lenght 
doesn't look sane to me. So how should this be fixed?

--
have fun,
alex