linux-kernel - Re: [PATCH] ARM: dts: rockchip: Add vdd

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Date:   Mon, 25 Mar 2019 13:30:16 +0100
From:   Heiko Stuebner <heiko@...ech.de>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     mka@...omium.org, ryandcase@...omium.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: dts: rockchip: Add vdd_logic to rk3288-veyron

Am Donnerstag, 21. März 2019, 21:19:44 CET schrieb Douglas Anderson:
> The vdd_logic rail controls the voltage supplied to misc logic on
> rk3288, including the voltage supplied to the memory controller.  The
> vcc logic is implemented by a PWM regulator.
> 
> Right now there are no consumers of vdd_logic on veyron but if anyone
> ever wants to try to add DDR Freq they'd need it.
> 
> Note that in the downstream Chrome OS kernel the PWM regulator has
> a voltage table with these points:
>   1350000 0%
>   1300000 10%
>   1250000 20%
>   1200000 31%
>   1150000 41%
>   1125000 46%
>   1100000 52%
>   1050000 62%
>   1000000 72%
>    950000 83%
> 
> The DDR Freq driver in the downstream kernel only uses some of those
> points, namely:
>   DDR3:  1200000, 1150000, 1100000, 1050000
>   LPDDR:          1150000, 1100000, 1050000
> 
> When adapting the downstream kernel to upstream I have opted to switch
> to using the "continuous" mode of the PWM regulator driver.  This was
> the only way I could get the upstream driver to achieve _exactly_ the
> same voltages as the downstream driver could.  Specifically note that
> the old driver in downstream Chrome OS 3.14 _didn't_ have the
> DIV_ROUND_CLOSEST_ULL() in the Rockchip PLL driver.  That means if I
> use the same (downstream) table I might end up with a duty cycle
> that's 1 larger than was used downstream, leading to a slightly
> different voltage.  Due to the way the rounding worked I couldn't even
> just adjust the "percent" by 1 for a given voltage level--certain duty
> cycles just aren't achievable with the upstream math for voltage
> tables.
> 
> Using continuous mode you can achieve the exact same duty cycle by
> simply adjusting the voltage you use by a tad bit.  The voltages that
> are equivalent to the ones used in the downstream kernel's table are:
>   1350000, 1304472, 1255691, 1200407, 1154878,
>   1128862, 1099593, 1050813, 1005285, 950000
> 
> Note that the top/bottom voltage is exactly the same just due to the
> way that continuous mode is calculated and the fact that I used those
> as anchors.  I didn't make any attempt to do the resistor math (as was
> done on rk3399-gru).
> 
> If anyone ever gets DDRFreq working on veyron upstream they should
> thus adjust the voltage specified in the DDRFreq operating points
> slightly (as per the above) to obtain the existing/tested values.  AKA
> you'd use:
>   DDR3:  1200407, 1154878, 1099593, 1050813
>   LPDDR:          1154878, 1099593, 1050813
> 
> A few other notes:
> - The "period" here (1994) is different than the "period" downstream
>   (2000) for similar reasons: there's a DIV_ROUND_CLOSEST_ULL() that
>   wasn't downstream.  With 1994 upstream comes up with the same value
>   (0x94) to program into the hardware that downstream put there.  As
>   far as I can tell 0x94 actually means 1993.27.
> - The duty cycle unit of 0x94 was picked by just matching the period
>   which nicely allows us to insert 0x7b as that value to program into
>   the hardware for 950mV.  The 0x7b was found by observing what the
>   downstream kernel calculated (not that the system can actually run
>   with vdd_log at 950 mV).
> - The downstream kernel can also be seen to program a different value
>   into the CTRL field.  Upstream achieves 0x0b and downstream 0x1b.
>   This is because the upstream commit bc834d7b07b4 ("pwm: rockchip:
>   Move the configuration of polarity") fixed a bug by adding "ctrl &=
>   ~PWM_POLARITY_MASK".  Downstream accidentally left bit 4 set.
>   Luckily this bit doesn't matter--it's only used when the PWM goes
>   inactive (AKA if it's in oneshot mode or is disabled) and we don't
>   do that for the PWM regulator.
> 
> I measured the voltage of vdd_log while adjusting it and found that
> with the upstream kernel voltage difference between requested and
> actual was 9.2 mV at 950 mV and 13.4 mV at 1350 mV with in-between
> voltages consistently showing ~1% error.  This error is likely
> expected as voltage can be seen to sag a bit when more load is put on
> the rail.
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

applied for 5.2

Thanks
Heiko