linux-kernel - Re: [PATCH v7 12/34] i2c: tegra: Use clk-bulk helpers

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Message-ID: <175e7f54-36f0-32c6-35a3-14c5b5e89e95@gmail.com>
Date:   Thu, 17 Sep 2020 18:01:56 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 12/34] i2c: tegra: Use clk-bulk helpers

17.09.2020 14:38, Thierry Reding пишет:
> On Wed, Sep 09, 2020 at 01:39:44AM +0300, Dmitry Osipenko wrote:
>> Use clk-bulk helpers and factor out clocks initialization into separate
>> function in order to make code cleaner.
>>
>> The clocks initialization now performed after reset-control initialization
>> in order to avoid a noisy -PROBE_DEFER errors on T186+ from the clk-bulk
>> helper which doesn't silence this error code. Hence reset_control_get()
>> now may return -EPROBE_DEFER on newer Tegra SoCs because they use BPMP
>> driver that provides reset controls and BPMP doesn't come up early during
>> boot. Previously rst was protected by the clocks retrieval and now this
>> patch makes dev_err_probe() to be used for the rst error handling.
>>
>> Suggested-by: Andy Shevchenko <andy.shevchenko@...il.com>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/i2c/busses/i2c-tegra.c | 187 ++++++++++++---------------------
>>  1 file changed, 67 insertions(+), 120 deletions(-)
> 
> This is tempting from a diffstat point of view, but the downside is that
> we can now no longer validate that all of the necessary clocks are given
> in device tree.
> 
> Previously the driver would fail to probe the I2C controller if any of
> the expected clocks were not defined in device tree, but now it's just
> going to continue without it and not give any indication as to what's
> wrong.

The clocks can't be missed randomly in a device-tree because they are a
part of the core tegra.dtsi

The tegra-i2c DT binding isn't converted to YAML, but once it will be,
then the dtbs_check will tell you about such obvious problems like a
missing mandatory property.

Even if clock is missing, then you won't miss this problem since I2C
shouldn't work in that case.

There is a Qualcomm I2C driver that already uses clk_bulk_get_all() and
doesn't worry about "accidentally" missing clocks.

It's still possible to add the clk-num checking, but it should be
unpractical. We could always add it later on if there will be a real
incident. Do you agree?