From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nicolin Chen Subject: Re: [PATCH v3 2/2] hwmon: ina3221: Read channel input source info from DT Date: Sat, 22 Sep 2018 17:38:42 -0700 Message-ID: <20180923003841.GA10071@Asurada-Nvidia.nvidia.com> References: <20180921223216.634-1-nicoleotsuka@gmail.com> <20180921223216.634-3-nicoleotsuka@gmail.com> <20180922184650.GB9092@Asurada> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Guenter Roeck Cc: jdelvare@suse.com, robh+dt@kernel.org, mark.rutland@arm.com, corbet@lwn.net, afd@ti.com, linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org List-Id: devicetree@vger.kernel.org On Sat, Sep 22, 2018 at 04:59:55PM -0700, Guenter Roeck wrote: > > > > + /* Disable channels if their inputs are disconnected */ > > > > + for (i = 0, mask = 0; i < INA3221_NUM_CHANNELS; i++) { > > > > + if (ina->inputs[i].disconnected) > > > > + mask |= INA3221_CONFIG_CHx_EN(i); > > > > + } > > > > > > Consequently, you should also _enable_ channels which are not explicitly disabled. > > > > The register has enabled all channels by default. So I felt it'd > > be neat to have disabling code only. My v1 actually had enabling > > part as well, but I can add it back if you think it'd be better. > > > > > This can be tricky since you'll have to distinguish non-DT and DT configuration > > > and retain the original configuration if no channel configuration data is available > > > from devicetree. > > For non-DT configurations, input->disconnected is always false by > > default unless someone adds config for it (through platform_data). > > If regmap_update_bits only does disabling like this version does, > > non-DT configurations will not get affected since mask = 0. Or if > > we change it to do both enabling and disabling, regmap_update_bits > > will still ignore since there's no register value changed, though > > it won't really hurt even if regmap writes correct configurations > > to the register. > > > > For DT configurations (without channel input source defined), it's > > like the same as non-DT configurations. As we have platforms only > > enabled ina3221 via DT while they don't have this new DT binding, > > the driver has to be backward compatible, so my change only sets > > input->disconnected=true when a status="disabled" is present, i.e. > > those platforms are treated as all channels getting enabled until > > they update their DTs. > I think your assumption may be that the chip is always in its reset state > when Linux is loaded. This is not necessarily the case; it may be > preconfigured by BIOS or ROMMON, or even by someone using i2cset before > loading the driver. If you add enable/disable functionality, you can > not make an assumption about the original state of the chip at probe time; > you have to read it from the chip itself. I see. That made a point. In that case, I think the simplest way is probably to do software reset before having configurations. The "disconnected" here is to describe the physical connection, not exact the switch control status because a channel could be connected but disabled. However, a channel would not be enabled if it's disconnected. So I think it'd be safe to just disable the disconnected channels here as this version does, meanwhile, I will add a soft reset to make sure all channels are enabled. Thanks Nicolin