Re: [PATCH 1/6] mach-bcm2835/core: add clkdev for uart1

[Lucas Stach <l.stach@pengutronix.de>]

Am Mittwoch, den 12.12.2018, 15:10 +0100 schrieb Rouven Czerwinski:
> Add a clkdev for uart1 which will be used on the Raspberry Pi 3.
> Double the clockrate since the ns16550 driver used for the uart will divide by
> 16, while the bcm2835 peripheral manual describes that the bcm2835 miniuart will
> only divide by 8.
> 
> > Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
> ---
>  arch/arm/mach-bcm283x/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/mach-bcm283x/core.c b/arch/arm/mach-bcm283x/core.c
> index f1dcda86f..66af76b09 100644
> --- a/arch/arm/mach-bcm283x/core.c
> +++ b/arch/arm/mach-bcm283x/core.c
> @@ -42,6 +42,12 @@ static int bcm2835_clk_init(void)
> >  	clk_register_clkdev(clk, NULL, "uart0-pl0110");
> >  	clkdev_add_physbase(clk, 0x20201000, NULL);
> >  	clkdev_add_physbase(clk, 0x3f201000, NULL);
> > +	/*
> > +	 * We double the clock rate since the 16550 will divide by 16
> > +	 * (instead of 8 required by the BCM2835 peripheral manual)
> +	 */

This is confusing. The clock is running at another rate. I would prefer
to do this adjustment in rpi_init_port() in the ns16550 driver, as
that's the point where the hardware deviation actually is.

Regards,
Lucas

> +	clk = clk_fixed("uart1-8250", 500 * 1000 * 1000);
> > +	clkdev_add_physbase(clk, 0x3f215040, NULL);
>  
> >  	clk = clk_fixed("bcm2835-cs", 1 * 1000 * 1000);
> >  	clk_register_clkdev(clk, NULL, "bcm2835-cs");

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