Re: [PATCH v2 2/4] doc: dt: add documentation for lpc1850-cgu clk driver

Joachim Eastwood
2015-05-13T07:57:18Z

On 13 May 2015 at 00:12, Michael Turquette <mturquette@linaro.org> wrote:
> Quoting Joachim Eastwood (2015-04-27 14:38:11)
>> Add DT binding documentation for lpc1850-cgu driver.
>>
>> Signed-off-by: Joachim Eastwood <manabian@gmail.com>
>> ---
>> .../devicetree/bindings/clock/lpc1850-cgu.txt | 138 +++++++++++++++++++++
>> 1 file changed, 138 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/clock/lpc1850-cgu.txt
>>
>> diff --git a/Documentation/devicetree/bindings/clock/lpc1850-cgu.txt b/Documentation/devicetree/bindings/clock/lpc1850-cgu.txt
>> new file mode 100644
>> index 000000000000..0b278ca6aee7
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/clock/lpc1850-cgu.txt
>> @@ -0,0 +1,138 @@
>> +* NXP LPC1850 Clock Generation Unit (CGU)
>> +
>> +The CGU generates multiple independent clocks for the core and the
>> +peripheral blocks of the LPC18xx. Each independent clock is called
>> +a base clock and itself is one of the inputs to the two Clock
>> +Control Units (CCUs) which control the branch clocks to the
>> +individual peripherals.
>> +
>> +The CGU selects the inputs to the clock generators from multiple
>> +clock sources, controls the clock generation, and routes the outputs
>> +of the clock generators through the clock source bus to the output
>> +stages. Each output stage provides an independent clock source and
>> +corresponds to one of the base clocks for the LPC18xx.
>> +
>> + - Above text taken from NXP LPC1850 User Manual.
>> +
>> +
>> +This binding uses the common clock binding:
>> + Documentation/devicetree/bindings/clock/clock-bindings.txt
>> +
>> +Required properties:
>> +- compatible:
>> + Should be "nxp,lpc1850-cgu"
>> +- reg:
>> + Shall define the base and range of the address space
>> + containing clock control registers
>> +- #clock-cells:
>> + Shall have value <1>. The permitted clock-specifier values
>> + are the base clock numbers defined below.
>> +- clocks:
>> + Shall contain a list of phandles for the external input
>> + sources to the CGU. The list shall be in the following
>> + order: xtal, 32khz, enet_rx_clk, enet_tx_clk, gp_clkin.
>> +- clock-indices:
>> + Shall be an ordered list of numbers defining the base clock
>> + number provided by the CGU.
>> +- clock-output-names:
>> + Shall be an ordered list of strings defining the names of
>> + the clocks provided by the CGU.
>> +
>> +Which base clocks that are available on the CGU depends on the
>> +specific LPC part. Base cloks are numbered from 0 to 27.
>
> s/cloks/clocks/
>
>> +
>> +Number: Name: Description:
>> + 0 BASE_SAFE_CLK Base safe clock (always on) for WWDT
>> + 1 BASE_USB0_CLK Base clock for USB0
>> + 2 BASE_PERIPH_CLK Base clock for Cortex-M0SUB subsystem,
>> + SPI, and SGPIO
>> + 3 BASE_USB1_CLK Base clock for USB1
>> + 4 BASE_CPU_CLK System base clock for ARM Cortex-M core
>> + and APB peripheral blocks #0 and #2
>> + 5 BASE_SPIFI_CLK Base clock for SPIFI
>> + 6 BASE_SPI_CLK Base clock for SPI
>> + 7 BASE_PHY_RX_CLK Base clock for Ethernet PHY Receive clock
>> + 8 BASE_PHY_TX_CLK Base clock for Ethernet PHY Transmit clock
>> + 9 BASE_APB1_CLK Base clock for APB peripheral block # 1
>> +10 BASE_APB3_CLK Base clock for APB peripheral block # 3
>> +11 BASE_LCD_CLK Base clock for LCD
>> +12 BASE_ADCHS_CLK Base clock for ADCHS
>> +13 BASE_SDIO_CLK Base clock for SD/MMC
>> +14 BASE_SSP0_CLK Base clock for SSP0
>> +15 BASE_SSP1_CLK Base clock for SSP1
>> +16 BASE_UART0_CLK Base clock for UART0
>> +17 BASE_UART1_CLK Base clock for UART1
>> +18 BASE_UART2_CLK Base clock for UART2
>> +19 BASE_UART3_CLK Base clock for UART3
>> +20 BASE_OUT_CLK Base clock for CLKOUT pin
>> +24-21 - Reserved
>> +25 BASE_AUDIO_CLK Base clock for audio system (I2S)
>> +26 BASE_CGU_OUT0_CLK Base clock for CGU_OUT0 clock output
>> +27 BASE_CGU_OUT1_CLK Base clock for CGU_OUT1 clock output
>> +
>> +BASE_PERIPH_CLK and BASE_SPI_CLK is only available on LPC43xx.
>> +BASE_ADCHS_CLK is only available on LPC4370.
>> +
>> +
>> +Example board file:
>> +
>> +/ {
>> + clocks {
>> + xtal: xtal {
>> + compatible = "fixed-clock";
>> + #clock-cells = <0>;
>> + clock-frequency = <12000000>;
>> + };
>> +
>> + xtal32: xtal32 {
>> + compatible = "fixed-clock";
>> + #clock-cells = <0>;
>> + clock-frequency = <32768>;
>> + };
>> +
>> + enet_rx_clk: enet_rx_clk {
>> + compatible = "fixed-clock";
>> + #clock-cells = <0>;
>> + clock-frequency = <0>;
>> + clock-output-names = "enet_rx_clk";
>> + };
>> +
>> + enet_tx_clk: enet_tx_clk {
>> + compatible = "fixed-clock";
>> + #clock-cells = <0>;
>> + clock-frequency = <0>;
>> + clock-output-names = "enet_tx_clk";
>> + };
>> +
>> + gp_clkin: gp_clkin {
>> + compatible = "fixed-clock";
>> + #clock-cells = <0>;
>> + clock-frequency = <0>;
>> + clock-output-names = "gp_clkin";
>> + };
>> + };
>> +
>> + soc {
>> + cgu: cgu@40050000 {
>> + compatible = "nxp,lpc1850-cgu";
>> + reg = <0x40050000 0x1000>;
>> + #clock-cells = <1>;
>> + clocks = <&xtal>, <&creg_clk 1>, <&enet_rx_clk>, <&enet_tx_clk>, <&gp_clkin>;
>> + clock-indices = <0>, <1>, <2>, <3>, <4>, <5>, <6>, <7>,
>> + <8>, <9>, <10>, <11>, <12>, <13>, <14>, <15>,
>> + <16>, <17>, <18>, <19>, <20>, <25>, <26>, <27>;
>> + clock-output-names = "base_safe_clk", "base_usb0_clk",
>> + "base_periph_clk", "base_usb1_clk",
>> + "base_cpu_clk", "base_spifi_clk",
>> + "base_spi_clk", "base_phy_rx_clk",
>> + "base_phy_tx_clk", "base_apb1_clk",
>> + "base_apb3_clk", "base_lcd_clk",
>> + "base_adchs_clk", "base_sdio_clk",
>> + "base_ssp0_clk", "base_ssp1_clk",
>> + "base_uart0_clk", "base_uart1_clk",
>> + "base_uart2_clk", "base_uart3_clk",
>> + "base_out_clk", "base_audio_clk",
>> + "base_cgu_out0_clk","base_cgu_out1_clk";
>
> Why do you need to use clock-indices?

Since the CGU can have up to 27 clock lines, but in this device not
all are used. So I use clock-indices so I don't need to have empty
entries in the clock-output-names array. I thought this was the
intended usage(?)

> Why do you need to use clock-output-names? If all of your clock
> consumers have nodes in DT then you can skip this and name them on the
> consuming side. See a further explanation here:
> http://lkml.kernel.org/r/<20150416192014.19585.9663@quantum>

Most of the clocks from the CGU goes to a CCU, but the CCU isn't the
real consumer. It's more like a clock router with a bunch of gates.

If you take a close look at the CCU driver you will notice that it
doesn't do clk_get on any of the clocks. My reason for doing this is
to not increase the usage counter on the CGU clock so that if there
are no consumer after a CCU the entire clock line up to the CGU can be
disabled. So this is the reason that the CCU driver uses a "special"
way to grab the clock output names from the CGU.

Hope this makes sense.

> Also note that providing a clock consumer node in the examples section
> of the binding is helpful when reviewing.

I'll add a consumer example in the next version.

regards,
Joachim Eastwood