Re: [lm-sensors] [PATCH] hwmon: (pmbus) Fix two issues

From: Guenter Roeck <guenter.roeck@ericsson.com>
To: lm-sensors@vger.kernel.org
Subject: Re: [lm-sensors] [PATCH] hwmon: (pmbus) Fix two issues
Date: Tue, 15 Nov 2011 02:42:13 +0000	[thread overview]
Message-ID: <20111115024213.GA28863@ericsson.com> (raw)
In-Reply-To: <1321249266-17071-1-git-send-email-Yuantian.Tang@freescale.com>

On Mon, Nov 14, 2011 at 09:28:40PM -0500, Tang Yuantian-B29983 wrote:
> Hi Guenter,
> 
> Please find my comments in line.
> 
> > -----Original Message-----
> > > > > SMBus block reads receive the block length as the first byte. 0x10
> > > > > = 16, which is the length of the ID for these chips, this is no
> > > I didn't write the driver, and don't have the device, but I think the
> > > driver is OK as is. The block length (0x10) is handled by the
> > > underlying bus driver, the device driver never gets to see it, if you
> > > properly call i2c_smbus_read_block_data() as you are supposed to.
> > >
> > I have eval boards for all chips supported by the driver (lots of kudos
> > to Intersil), so the driver was tested and is known to work for all chips
> > it currently supports. Intersil told me that they don't update the
> > firmware after they released a chip, so we can be sure that the firmware
> > version on all chips of the same type is the same, and we don't have to
> > look for version specific behavior.
> > 
> > I agree that we should not replace the SMBus block read with SMBus I2C
> > block read. The I2C bus driver should really implement SMBus block read
> > command support.
> > 
> > There are some I2C bus drivers which can not support SMBus block reads
> > due to chip limitations, such as the Sibyte driver, but if the driver can
> > support SMBus I2C block reads it should possible to support SMBus block
> > reads as well. As far as I can see, the only driver supporting SMBUS I2C
> > block reads but not SMBUS block reads is scx200_acb. That seems to be an
> > oversight (or maybe laziness ;), and should be easy to fix.
> > 
> [Yuantian:] what platform are you testing on?
> What I see is most i2c bus drivers don't support "SMBus block".

Actually, almost all drivers support it, via SMBus emulation code. And if a driver
supports SMBus I2C block commands, there is no technical reason why it should not
support SMBus block commands.

To answer your question, PC based systems, PowerPC based systems, Octeon based
systems, and a Sibyte based system (where block commands don't work).

Guenter

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