On 9/23/20 9:05 PM, Kurt Van Dijck wrote:
> On wo, 23 sep 2020 16:55:13 +0200, Matthias Weißer wrote:
>> Hi
>>
>> I currently try to get a MCP2518FD to work on our custom iMX6ULL based
>> hardware. I use the driver currently in linux-can-next backported to
>> our v5.4 kernel
>>
>> DT:
>> can0: can@0 {
>> compatible = "microchip,mcp25xxfd";
>> reg = <0>;
>> clocks = <&can3_osc>;
>> spi-max-frequency = <85000000>;
> I did not experience issues by using the real 20MHz upper limit here.
Not quite...
>> interrupts-extended = <&gpio1 18 IRQ_TYPE_LEVEL_LOW>;
>> status = "okay";
>> };
>>
>> # dmesg | grep mcp
>> [ 3.706085] mcp25xxfd spi1.0 can0: MCP2518FD rev0.0 (-RX_INT
>> -MAB_NO_WARN +CRC_REG +CRC_RX +CRC_TX +ECC -HD c:20.00MHz m:8.50MHz
>> r:8.50MHz e:0.00MHz) successfully initialized.
>
> off-topic:
> Variscite deploys a 20HHz oscillator, which brings the max spi frequency
> down to +/- 8.5MHz.
> After discussion with Thomas Kopp, I learned that microchip uses a 40MHz
> oscillator, to arrive (close to) 20MHz spi freq.
> Would you not use a 40MHz oscillator too?
According to the debug output the can3_osc is 20 MHz. According to the datasheet
this makes 10 MHz SPI clock, however it turns out, you can only use 85% of that
to avoid stability problems. The driver takes care of the 85%, so you don't have
to specify this in the DT.
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 |
Attachment:
signature.asc
Description: OpenPGP digital signature
