From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH v8 2/5] i2c: Add STM32F4 I2C driver Date: Thu, 12 Jan 2017 13:03:09 +0100 Message-ID: <20170112120309.fmrt2lwz3vklqmti@pengutronix.de> References: <1483607246-14771-1-git-send-email-cedric.madianga@gmail.com> <1483607246-14771-3-git-send-email-cedric.madianga@gmail.com> <20170111082208.vzu7xgpd4eakyldl@pengutronix.de> <20170111153940.dtxzvtdici3r7l54@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: M'boumba Cedric Madianga Cc: devicetree@vger.kernel.org, Alexandre Torgue , Wolfram Sang , linux-kernel@vger.kernel.org, Linus Walleij , Patrice Chotard , Russell King , Rob Herring , linux-i2c@vger.kernel.org, Maxime Coquelin , linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org Hello Cedric, On Thu, Jan 12, 2017 at 12:23:12PM +0100, M'boumba Cedric Madianga wrote: > 2017-01-11 16:39 GMT+01:00 Uwe Kleine-K=F6nig : > > On Wed, Jan 11, 2017 at 02:58:44PM +0100, M'boumba Cedric Madianga wrot= e: > >> 2017-01-11 9:22 GMT+01:00 Uwe Kleine-K=F6nig : > >> > This is surprising. I didn't recheck the manual, but that looks very > >> > uncomfortable. > >> > >> I agree but this exactly the hardware way of working described in the > >> reference manual. > > > > IMHO that's a hw bug. This makes it for example impossible to implement > > SMBus block transfers (I think). > = > This is not correct. > Setting STOP/START bit does not mean the the pulse will be sent right now. > Here we have just to prepare the hardware for the 2 next pulse but the > STOP/START/ACK pulse will be generated at the right time as required > by I2C specification. > So SMBus block transfer will be possible. A block transfer consists of a byte that specifies the count of bytes yet to come. So the device sends for example: 0x01 0xab So when you read the 1 in the first byte it's already too late to set STOP to get it after the 2nd byte. Not sure I got all the required details right, though. Best regards Uwe -- = Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | http://www.pengutronix.de/ |