From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH 1/2] i2c: tegra: Maintain CPU endianness Date: Thu, 22 Jan 2015 20:18:34 +0300 Message-ID: <54C130EA.2050505@gmail.com> References: <1421756555-20266-1-git-send-email-digetx@gmail.com> <20150122074001.GB427@ulmo> <54C115D1.10206@gmail.com> <54C12010.8040504@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <54C12010.8040504-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Alexandre Courbot , Thierry Reding Cc: 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 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 origin= ates >>>> from the I2C controller? >> >> No, i2c_readl returns value in CPU endianness, so it's correct. But = for >> i2c_writel should be used le32_to_cpu(), since it takes value in CPU= 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 bytes >>> 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 abo= ut >> endianness and produces expected result, since I2C message is char a= rray. >> > I'll spend some more time reviewing, to see if nullifying should go a= s separate > patch. > Well, I2C_FIFO_STATUS returns 8-bit value. The rest of bits very likely= to be=20 RAZ, however I don't see anything on it in documentation. In that case = it won't=20 cause any problems with LE value and nullifying is only needed for BE m= ode. --=20 Dmitry