On 11/11/19 9:31 PM, Drew Fustini wrote: >> On Mon, Nov 11, 2019 at 11:28:14AM +0100, Marc Kleine-Budde wrote: >>> I successfully got a mcp25625 (which is basically a mcp2515 with >>> internal phy) running on a rapsi using the frequency printed on the >>> oscillator in the DT-overlay. >> >> I came across this patch by Andy on the linux-can archives: >> >> [PATCH v2] can: mcp251x: Get rid of legacy platform data >> https://www.spinics.net/lists/linux-can/msg02407.html >> >> The description: >> Instead of using legacy platform data, switch to use device properties. >> For clock frequency we are using well established clock-frequency property. >> >> I reads the clock-frequency property from device tree: >> >> freq = clk_get_rate(clk); >> - if (freq == 0 && pdata) >> - freq = pdata->oscillator_frequency; >> + if (freq == 0) >> + device_property_read_u32(&spi->dev, "clock-frequency", &freq); >> >> >> I feel like this is currently missing from mcp251x.c. I don't see how it is >> reading the clock frequency from Device Tree as I don't see any code in the >> current mcp251x.c to read device tree properties. >> >> I would appreciate any insights to improve my understanding. > > Also, I meant to ask as to why the clock for MCP2515 Oscillator comes > from the spi device: > clk = devm_clk_get(&spi->dev, NULL); The mcp2515 is a SPI chip and it's clocked by an external oscillator. This is described via the DT. Looking at a random board in the kernel: arch/arm/boot/dts/at91-sama5d4_ma5d4.dtsi > clk20m: clk20m { > compatible = "fixed-clock"; > #clock-cells = <0>; > clock-frequency = <20000000>; > clock-output-names = "clk20m"; > }; [...] > spi1: spi@fc018000 { > cs-gpios = <&pioB 22 0>, <&pioB 23 0>, <0>, <0>; > status = "okay"; > > can0: can@0 { > compatible = "microchip,mcp2515"; > reg = <0>; > clocks = <&clk20m>; This is a "link" (called phandle in the DT-world) to the "clk20m" node above. That node has a "clock-frequency" property of 20MHz. > interrupt-parent = <&pioE>; > interrupts = <6 IRQ_TYPE_EDGE_RISING>; > spi-max-frequency = <10000000>; > }; By "devm_clk_get()" the driver first gets a reference to the clock and by "clk_get_rate()" the frequency. This is generic non-spi specific DT handling. > line 1034 from: > https://elixir.bootlin.com/linux/latest/source/drivers/net/can/spi/mcp251x.c#L1034 > > It seem like there should be separate clocks for the SPI frequency and > the MCP2515 oscillator frequency. The SPI frequency, to be more precise the maximal SPI frequency the mcp2515 supports on that particular board, is specified by the property "spi-max-frequency" it's handled by the SPI core code. hth, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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