From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH 1/2] i2c: tegra: Maintain CPU endianness Date: Fri, 23 Jan 2015 16:27:07 +0300 Message-ID: <54C24C2B.1070907@gmail.com> References: <1421756555-20266-1-git-send-email-digetx@gmail.com> <20150122074001.GB427@ulmo> <54C115D1.10206@gmail.com> <54C12010.8040504@gmail.com> <54C130EA.2050505@gmail.com> <20150123094552.GD3835@ulmo> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20150123094552.GD3835@ulmo> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Thierry Reding Cc: Alexandre Courbot , Wolfram Sang , Stephen Warren , Laxman Dewangan , Ben Dooks , Bob Mottram , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Linux Kernel Mailing List List-Id: linux-i2c@vger.kernel.org 23.01.2015 12:45, Thierry Reding =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > On Thu, Jan 22, 2015 at 08:18:34PM +0300, Dmitry Osipenko wrote: >> 22.01.2015 19:06, Dmitry Osipenko =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>> 22.01.2015 18:22, Dmitry Osipenko =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> 22.01.2015 10:55, Alexandre Courbot =D0=BF=D0=B8=D1=88=D0=B5=D1=82= : >>>>> On Thu, Jan 22, 2015 at 4:40 PM, Thierry Reding >>>>> wrote: >>>>>> >>>>>> Should this not technically be le32_to_cpu() since the data orig= inates >>>>> >from the I2C controller? >>>> >>>> No, i2c_readl returns value in CPU endianness, so it's correct. Bu= t for >>>> i2c_writel should be used le32_to_cpu(), since it takes value in C= PU endianness. >>>> It's my overlook, V2 is coming. >>>> >>>>>> >>>>>> Why does this have to be initialized to 0 now? >>>>> >>>>> I suspect this is because we are going to memcpy less than 4 byte= s >>>>> into it, but I cannot figure out how that memcpy if guaranteed to >>>>> produce the expected result for both endiannesses. >>>>> >>>> That's correct. Memcpy is working with bytes, so it doesn't care a= bout >>>> endianness and produces expected result, since I2C message is char= array. >>>> >>> I'll spend some more time reviewing, to see if nullifying should go= as separate >>> patch. >>> >> Well, I2C_FIFO_STATUS returns 8-bit value. The rest of bits very lik= ely to >> be RAZ, however I don't see anything on it in documentation. In that= case it >> won't cause any problems with LE value and nullifying is only needed= for BE >> mode. > > What does I2C_FIFO_STATUS have to do with anything? > > My point was more that we already tell hardware how much data is to b= e > transferred (via the packet header in tegra_i2c_xfer_msg()), hence th= e > hardware shouldn't care whether the FIFO is padded with random data o= r > zeros. > > Thierry > Got your point. I was thinking it's expected behavior, but now I'll ela= borate=20 this more. --=20 Dmitry