linux-kernel - Re: [PATCH v2,1/3] meson_uart: expose CLKID

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Date:   Tue, 28 Mar 2017 23:24:15 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Helmut Klein <hgkr.klein@...il.com>, mturquette@...libre.com,
        sboyd@...eaurora.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH v2,1/3] meson_uart: expose CLKID_UARTx

Hi Jerome,

On Tue, Mar 28, 2017 at 9:14 PM, Jerome Brunet <jbrunet@...libre.com> wrote:
> On Tue, 2017-03-28 at 20:18 +0200, Helmut Klein wrote:
>> i know for sure that the bluetooth chip of my system is connected to
>> uart_A. so this clock must be exposed.
>>
>> i don't know if the other 2 uarts are used on other hardware. so i will
>> remove them from my patch.
>
> What I meant is device trees "upstream".
> I would expect such patch as part of a series to add support for your board in
> device-tree, with its bluetooth chipset.
are you sure about this? Helmut is configuring the core clock of the
UART controller(s) here. we have the same thing for many other drivers
as well (MMC, SAR ADC, I2C, SPI, ethernet, you name it...) - these
clocks are not part of a device specific .dts but rather the SoC
specific dts (for example meson-gxbb.dtsi - because these clocks are
not board specific).
I guess most boards are not affected because the bootloader simply
enables the UART0 core/gate clock and keeps it enabled when booting
the kernel. additionally our clock gates are marked with
CLK_IGNORE_UNUSED so if the bootloader keeps the gates enabled then
we're not disabling it either.

> I think it would better to drop this patch from the series.
> You can either keep it for your personal work, or send it again when upstreaming
> the support for your board and/or add the support for the bluetooth chip.
if we decide to pass the core/gate clock directly in SoC.dtsi then we
should think about doing it for all three non-AO UARTs (uart_a, uart_b
and uart_c).
we can test uart_b on GPIODV_24 and GPIODV_25 on the Khadas VIM board
for example (pins 22 and 23 on the header, default mode of these pins
is i2c_sck_a and i2c_sda_a, but we can re-configure it).
uart_c unfortunately cannot be tested on the Khadas VIM board since
it's only routed to GPIOX_8 and GPIOX_9 which are hard-wired to the
bluetooth module's PCM pins (BTPCM_DOUT and BTPCM_DIN).

for Helmut this would mean that instead of dropping this patch (or
dropping CLKID_UART1 and CLKID_UART2 from this patch) he would rather
have to *add* another patch (for meson-gxbb.dtsi and meson-gxl.dtsi)
which passes the core clocks to the corresponding UART controllers
(similar to the CLKID_SD_EMMC_ clocks).


Regards,
Martin


[0] http://lxr.free-electrons.com/source/drivers/clk/meson/clkc.h?v=4.10#L110