From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vaibhav Hiremath Subject: Re: [RFC]: Supporting PIO mode of operation in i2c_msg->flags Date: Sun, 14 Jun 2015 17:42:31 +0530 Message-ID: <557D6FAF.1050408@linaro.org> References: <5562EF9D.1090403@linaro.org> <20150611234118.GA1534@katana> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150611234118.GA1534@katana> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Wolfram Sang Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On Friday 12 June 2015 05:11 AM, Wolfram Sang wrote: >> Current implementation: >> -------------------- >> >> Everyone probably does have their own custom implementation for this. >> Or some other mechanism to achieve this (may be hardware support). > > Do you have examples? It is easier to look at code. > As I mentioned in the "Problem Statement", I2C interface for PMIC may need to be used at the end of poweroff sequence where you cannot afford to sleep/schedule, as interrupt has been disabled. Earlier I was working on OMAP platform, where I remember we had implemented something for such requirement, but as I am not in TI anymore, I can not access the internal code. Let me check whether I can share the current marvell codebase outside. >> /* We can also check i2c_check_functionality(adap,I2C_FUNC_PIO) */ >> if (msg->flags & I2C_M_PIO) { >> /* PIO mode operation */ >> } else { >> /* non-pio mode of operation */ >> } > > I'd rather let the core decide. Like introduce a master_xfer_nosleep > callback and let the core use the standard or the nosleep one. We'd need > the same for smbus as well. > > This leads to the question if we need a M_FLAG or expose the *_nosleep > functions directly? > I thought of it, but did not convince myself after looking at the usage of this. This function would be used only when interrupt is disabled. > And I wonder about the demand for it. There are a number of SoCs with > designated I2C cores for the PMIC which do automated transfers. > This is exactly the same reason I did not propose it as a core change. as I feel that the use of this is very minimal and with M_FLAG driver can very well handle it. Thanks, Vaibhav