On 9/17/20 10:30 AM, Marc Kleine-Budde wrote: >> The results were clear, there is some SPI issue that prevents me >> specifying above 8.8Mhz, even if the effective speed is detected to be the same. > > Probably interger arithmetics :) > > 600 MHz / 8.823529 Mhz > > 600000000 / 8823529 = 68.0000031733 -> 69 > > The SPI host driver only supports even dividers. > > -> 70 > > 600 MHz / 70 = 8.57 MHz > > but your SPI host controller selects 8.33MHz... On the H3 it works as expected: > [ 7.937043] mcp25xxfd spi0.0 can0: MCP2518FD rev0.0 (+RX_INT -MAB_NO_WARN +CRC_REG +CRC_RX +CRC_TX +ECC -HD c:20.00MHz m:8.82MHz r:8.82MHz e:8.57MHz) successfully initialized. Request 8.82MHz -> Effective 8.57MHz If you want 8.82MHz, you have to specify"spi-max-frequency = <8823530>;" in the DT. This results in: > [ 8.074548] mcp25xxfd spi0.0 can0: MCP2518FD rev0.0 (+RX_INT -MAB_NO_WARN +CRC_REG +CRC_RX +CRC_TX +ECC -HD c:20.00MHz m:8.82MHz r:8.82MHz e:8.82MHz) successfully initialized. 600000000 / 8823530 = 67,9999954667 -> 68 600 MHz / 68 = 8.82 MHz regards. 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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