linux-kernel - RE: [PATCH] i2c/busses: (mpc) Add support for SMBUS_READ_BLOCK

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Date:	Thu, 1 Dec 2011 07:06:20 +0000
From:	Tang Yuantian-B29983 <B29983@...escale.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	"guenter.roeck@...csson.com" <guenter.roeck@...csson.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Huang Changming-R66093 <r66093@...escale.com>
Subject: RE: [PATCH] i2c/busses: (mpc) Add support for SMBUS_READ_BLOCK_DATA

Hi,

Has the patch been accepted?

Regards,
Yuantian

> -----Original Message-----
> From: Jean Delvare [mailto:khali@...ux-fr.org]
> Sent: 2011年11月17日 3:19
> To: sun york-R58495
> Cc: guenter.roeck@...csson.com; Tabi Timur-B04825; linux-
> i2c@...r.kernel.org; linux-kernel@...r.kernel.org; Tang Yuantian-B29983
> Subject: Re: [PATCH] i2c/busses: (mpc) Add support for
> SMBUS_READ_BLOCK_DATA
> 
> On Wed, 16 Nov 2011 11:15:15 -0800, York Sun wrote:
> > On Wed, 2011-11-16 at 20:10 +0100, Jean Delvare wrote:
> > > On Wed, 16 Nov 2011 10:20:38 -0800, York Sun wrote:
> > > > On Wed, 2011-11-16 at 19:09 +0100, Jean Delvare wrote:
> > > > > Your thinking is too focused on I2C block reads (or even block
> > > > > read of data over the network or on disk). SMBus block read is
> > > > > something completely different. It's not about reading 200 bytes
> > > > > of data and receiving it in 16-byte chunks (I2C block read works
> > > > > that way, on EEPROMs in particular.) There is no "data length"
> > > > > and "block size" to compare to each other. It's about reading
> > > > > the value of _one_ register and this value happens to be
> > > > > multi-byte. There is typically _no_ register pointer increment
> > > > > (automatic or not) involved as can happen with EEPROMs. If an
> > > > > SMBus block read from register N returns 10 bytes, you're not
> > > > > going to read the next 10 bytes from register N+10. There are no
> > > > > "next 10 bytes" to read, and register N+10 is something
> completely unrelated.
> > > > >
> > > > > And for this reason, it is not possible to mix SMBus block reads
> > > > > with byte reads, as can be done with I2C block reads.
> > > > >
> > > > > Also note that there is a limit of 32 bytes for SMBus block
> > > > > transfers, per SMBus specification. All slaves and masters must
> comply with it.
> > > > >
> > > > > I hope I managed to clarify the case this time...
> > > >
> > > > You have made it much clear. If block size is fixed and block read
> > > > cannot mix with byte read, shall we do this
> > > >
> > > > if length < block_size
> > > >    read block_size
> > > > else {
> > > >    while (length) {
> > > >        read block_size
> > > >        length -= block_size
> > > >    }
> > >
> > > Which part of
> > >
> > >   There is no "data length" and "block size" to compare to each other.
> > >
> > > did you not understand?
> >
> > For example, if the length is 40 and the block size is 32, are you
> > going to read 32, 72 byte or 64 byte?
> 
> The length is not 40. Which part of
> 
>   Also note that there is a limit of 32 bytes for SMBus block transfers,
>   per SMBus specification. All slaves and masters must comply with it.
> 
> did you now understand?
> 
> Really, please. I understand you're only trying to help and understand
> the patch, but at some point, if you have zero knowledge about the topic,
> you're not the right person to review the patch, period. You are still
> welcome to test the patch if you can and want, that's a completely
> different task.
> 
> --
> Jean Delvare


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