From: heiko@sntech.de (Heiko Stübner)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64: dts: rockchip: add i2c nodes for rk3399
Date: Sat, 18 Jun 2016 14:01:08 +0200 [thread overview]
Message-ID: <1633653.D0508meTWe@diego> (raw)
In-Reply-To: <1463429371-10950-1-git-send-email-dianders@chromium.org>
Am Montag, 16. Mai 2016, 13:09:31 schrieb Douglas Anderson:
> From: David Wu <david.wu@rock-chips.com>
>
> We've got 9 (count em!) i2c controllers on rk3399, some of which are in
> the PMU power domain and some of which are normal peripherals. Add them
> all to the main rk3399 dtsi file so future patches can turn them on in
> the board dts files.
>
> Note: by default we try to set the i2c clock rate to 200 MHz so that we
> can achieve good i2c functional clock rates. 200 MHz gives us the
> ability to make very close to 100 kHz / 400 kHz / 1 MHz rates. If
> boards want to tune clock rates further they can always override.
> Possibly boards could want to tune this if:
> - they wanted to save an infinitesimal amount of power and they knew
> their i2c bus was slow anyway. Since we gate the functional clock
> when the i2c bus is not active, power savings would only be while i2c
> transfers were happening and probably won't be very big anyway.
> - they wanted to eek out a bit more speed by carefully tuning the source
> clock to make divisions work out perfectly, accounting for the rise /
> fall time measured on an actual board.
>
> Note also that we still request 200 MHz for the PMU i2c busses even
> though we expect that we won't make that exactly (currently PPLL is 676
> MHz which gives us 169 MHz).
>
> Signed-off-by: David Wu <david.wu@rock-chips.com>
> Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
> [dianders: wrote desc; put in assigned-clocks; reordered nodes]
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
applied to my dts64 branch for 4.8
Thanks
Heiko
prev parent reply other threads:[~2016-06-18 12:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-16 20:09 [PATCH] arm64: dts: rockchip: add i2c nodes for rk3399 Douglas Anderson
2016-05-19 8:09 ` David.Wu
2016-06-18 12:01 ` Heiko Stübner [this message]
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