linux-kernel - Re: [PATCH] thermal: imx: interpret fsl,tempmon-data through nvmem

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Date:   Tue, 4 Jul 2017 14:51:18 +0300
From:   Leonard Crestez <leonard.crestez@....com>
To:     Shawn Guo <shawnguo@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        "Eduardo Valentin" <edubezval@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Mark Rutland" <mark.rutland@....com>,
        Lothar Waßmann <LW@...O-electronics.de>,
        Fabio Estevam <fabio.estevam@....com>
CC:     Dong Aisheng <aisheng.dong@....com>, <devicetree@...r.kernel.org>,
        "Bai Ping" <ping.bai@....com>, Anson Huang <Anson.Huang@....com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Octavian Purdila <octavian.purdila@....com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] thermal: imx: interpret fsl,tempmon-data through nvmem

On Mon, 2017-06-19 at 16:40 +0300, Leonard Crestez wrote:
> On imx6sx accessing the ocotp memory area directly is wrong because the
> ocotp clock needs to be enabled first. Fix this by reinterpreting the
> fsl,tempmon-data phandle as a reference to a nvmem_device and doing all
> the read through that.
> 
> This clock requirement does not apply to older imx6qdl chips because
> there the ocotp access clock (clk_ipg_s) is always enabled.
> 
> This is visible by comparing the "System Clocks, Gating, and Override"
> tables (OCOTP rows) in the 6DQ and 6SX manuals:
> http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX6SXRM.pdf
> http://www.nxp.com/assets/documents/data/en/reference-manuals/IMX6DQRM.pdf
> 
> This happens to work right now without this patch because the ocotp
> clock might be enabled for some other reason. In particular it might be
> enabled from the bootloader and it only gets disabled late during boot
> in clk_disable_unused, after imx-thermal has completed probing.
> 
> If imx-thermal is compiled as a module then the system can hang on
> probe.
> 
> This makes IMX_THERMAL depend on NVMEM_IMX_OCOTP but that driver seems
> be already available for all chips that contain tempmon so it's
> acceptable.
> 
> Reported-by: Lothar Waßmann <LW@...O-electronics.de>
> Signed-off-by: Leonard Crestez <leonard.crestez@....com>
> 
> ---
> 
> This was reported as a comment to a patch adding tempmon support for
> imx6ul (which is very similar to imx6sx). Since it already affects a
> supported chip this patch is sent as a separate bugfix.
> 
> Link: https://lkml.org/lkml/2017/6/9/578
> 
> There are various other ways to fix this problem. The main advantage of
> this solution is that it does not add a new binding but rather preserves
> compatibility with old DTBs. It also aligns with the idea that
> devicetree describes hardware relationships rather than a specific linux
> implementation.
> 
> An alternative would have been to add a nvmem-cells binding to imx-thermal and
> use that if available instead of fsl,tempmon-data. It might not be good to
> sidestep the official nvmem bindings, the devicetree people were added so that
> they have an opportunity to object.
> 
> In theory the "thermal grade" is a two-bit quantity and might be a
> candidate for using a cell with a "bits" binding. However this causes
> the nvmem core to issue reads of length and alignment less than 4 to the
> imx-ocotp driver so additional fixes might be required.
> 

It's been two weeks without a reply, any advice on how to proceed?
Since the original message is quite long I will summarize the main
question:

Is it OK to reinterpret the fsl,tempmon-data property as a nvmem
reference instead of a "raw" syscon regmap?

--
Regards,
Leonard