linux-kernel - Re: [PATCH v4 3/6] thermal: tsens: Rename tsens-8996 to tsens-v2 for reuse

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Message-ID: <CAP245DUG=wXApk6BVmaaUyTRBDaiPc0x4EDh3KS2ZfMxPQowkg@mail.gmail.com>
Date:   Wed, 4 Jul 2018 18:08:27 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        smohanad@...eaurora.org,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] thermal: tsens: Rename tsens-8996 to tsens-v2 for reuse

On Tue, Jul 3, 2018 at 12:23 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Mon 02 Jul 05:44 PDT 2018, Amit Kucheria wrote:
>
> > The TSENS block inside the 8996 is internally classified as version 2 of
> > the IP. Several other SoC families use this block and can share this code.
> >
> > We rename get_temp() to reflect that it can be used across the v2 family.
> >
> > Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> > ---
> >  drivers/thermal/qcom/Makefile                     |  2 +-
> >  drivers/thermal/qcom/{tsens-8996.c => tsens-v2.c} | 26 ++++++++---------------
> >  2 files changed, 10 insertions(+), 18 deletions(-)
> >  rename drivers/thermal/qcom/{tsens-8996.c => tsens-v2.c} (66%)
> >
> > diff --git a/drivers/thermal/qcom/Makefile b/drivers/thermal/qcom/Makefile
> > index 2cc2193..a821929 100644
> > --- a/drivers/thermal/qcom/Makefile
> > +++ b/drivers/thermal/qcom/Makefile
> > @@ -1,2 +1,2 @@
> >  obj-$(CONFIG_QCOM_TSENS)     += qcom_tsens.o
> > -qcom_tsens-y                 += tsens.o tsens-common.o tsens-8916.o tsens-8974.o tsens-8960.o tsens-8996.o
> > +qcom_tsens-y                 += tsens.o tsens-common.o tsens-8916.o tsens-8974.o tsens-8960.o tsens-v2.o
> > diff --git a/drivers/thermal/qcom/tsens-8996.c b/drivers/thermal/qcom/tsens-v2.c
> > similarity index 66%
> > rename from drivers/thermal/qcom/tsens-8996.c
> > rename to drivers/thermal/qcom/tsens-v2.c
> > index e1f7781..2eca7ff 100644
> > --- a/drivers/thermal/qcom/tsens-8996.c
> > +++ b/drivers/thermal/qcom/tsens-v2.c
> > @@ -1,27 +1,18 @@
> > +// SPDX-License-Identifier: GPL-2.0
> >  /*
> >   * Copyright (c) 2015, The Linux Foundation. All rights reserved.
> > - *
> > - * This program is free software; you can redistribute it and/or modify
> > - * it under the terms of the GNU General Public License version 2 and
> > - * only version 2 as published by the Free Software Foundation.
> > - *
> > - * This program is distributed in the hope that it will be useful,
> > - * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > - * GNU General Public License for more details.
> > - *
> > + * Copyright (c) 2018, Linaro Limited
> >   */
> >
> > -#include <linux/platform_device.h>
> >  #include <linux/regmap.h>
> >  #include "tsens.h"
> >
> > -#define STATUS_OFFSET        0x10a0
> > -#define LAST_TEMP_MASK       0xfff
> > +#define STATUS_OFFSET                0xa0
>
> This is not backwards compatible with present day dts files, you need to
> keep this effectively 0x10a0 when the memory region isn't split in two.

Argh!! Good catch.

> Perhaps you can just offset the ioremap by 4k when there's only one
> region?

That'll cause problems when we want to access some features exposed in
the other register bank through the common get_temp_tsens_v2 function.
The SW reset bit is in there that I'd like to add support for, for
example.

I can see a few other ways to detect this at runtime. None of them
look pretty but option 3 looks least ugly at least to me. Any
preferences?

1. Don't try to combine get_temp for 8996 with other v2 platforms.
This would mean retaining a separate ops_8996, pointing to a custom
get_temp(). We end up with two copies of the function.

2. In get_temp_tsens_v2(), check for number of regions but this has an
overhead for each temperature read.

     struct platform_device *op = of_find_device_by_node(tmdev->dev->of_node);
     if (op->num_resources > 1)
        status_offset = 0xa0;
     else
        status_offset = 0x10a0;
     Read temperature(status_offset);

3. Restrict to init time (ideal) by storing the status_offset to
struct tsens_device. This is then used directly in
get_temp_generic_v2() to determine the actual address. This should
work for 8996, 8916 and 8974 which all have a single memory region
iomapp'ed. The last two don't even need this value since they have
their own get_temp functions. See diff attached.

I have to ask: Are there really devices in the field that rely on the
existing *upstream* code and DT? If not, could we consider deprecating
the "qcom,msm8996-tsens" property immediately or at least mark it for
future removal?

Regards,
Amit

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