linux-kernel - [PATCH RFC v1 0/3] clk: meson: rounding for fast clocks on 32-bit SoCs

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Message-Id: <20210517203724.1006254-1-martin.blumenstingl@googlemail.com>
Date:   Mon, 17 May 2021 22:37:21 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     mturquette@...libre.com, sboyd@...nel.org, narmstrong@...libre.com,
        jbrunet@...libre.com, linux-clk@...r.kernel.org
Cc:     khilman@...libre.com, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH RFC v1 0/3] clk: meson: rounding for fast clocks on 32-bit SoCs

On the 32-bit Amlogic Meson8/8b/8m2 SoCs we run into a problem with the
fast HDMI PLL and it's OD (post-dividers). This clock tree can run at
up to approx. 3GHz.
This however causes a problem, because these rates require BIT(31) to
be usable. Unfortunately this is not the case with clk_ops.round_rate
on 32-bit systems. BIT(31) is reserved for the sign (+ or -).

clk_ops.determine_rate does not suffer from this limitation. It uses
an int to signal any errors and can then take all availble 32 bits for
the clock rate.

I am sending this as RFC to start a discussion whether:
- this is a good way to solve it?
- what are the alternatives?
- getting some feedback on areas that need to be improved

As always: any feedback is welcome!

Thank you!
Martin

Martin Blumenstingl (3):
  clk: divider: Add re-usable determine_rate implementations
  clk: meson: regmap: switch to determine_rate for the dividers
  clk: meson: pll: switch to determine_rate for the PLL ops

 drivers/clk/clk-divider.c      | 39 +++++++++++++++++++++++++++++++++-
 drivers/clk/meson/clk-pll.c    | 26 +++++++++++++----------
 drivers/clk/meson/clk-regmap.c | 19 ++++++++---------
 include/linux/clk-provider.h   |  6 ++++++
 4 files changed, 68 insertions(+), 22 deletions(-)

-- 
2.31.1