From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: [PATCH] i2c/busses: (mpc) Add support for SMBUS_READ_BLOCK_DATA Date: Wed, 16 Nov 2011 20:10:48 +0100 Message-ID: <20111116201048.4b7877dd@endymion.delvare> References: <1321338462-6138-1-git-send-email-guenter.roeck@ericsson.com> <1321464509.7847.41.camel@oslab-l1> <1321464968.2309.384.camel@groeck-laptop> <1321466135.7847.55.camel@oslab-l1> <20111116190954.67c846fc@endymion.delvare> <1321467638.7847.73.camel@oslab-l1> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1321467638.7847.73.camel@oslab-l1> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: York Sun Cc: guenter.roeck-IzeFyvvaP7pWk0Htik3J/w@public.gmane.org, Tabi Timur-B04825 , linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, B29983-KZfg59tc24xl57MIdRCFDg@public.gmane.org List-Id: linux-i2c@vger.kernel.org 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? -- Jean Delvare