Re: [PATCH v2 07/16] ARM: at91: import early_udelay from at91bootstrap

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH v2 07/16] ARM: at91: import early_udelay from at91bootstrap
Date: Wed, 20 Feb 2019 10:20:32 +0100	[thread overview]
Message-ID: <20190220092032.qgmere6l5haeqlyb@pengutronix.de> (raw)
In-Reply-To: <20190219172150.11901-8-a.fatoum@pengutronix.de>

On Tue, Feb 19, 2019 at 06:21:41PM +0100, Ahmad Fatoum wrote:
> For use by the incoming at91bootstrap DDRAMC initialization code,
> this commit provides an early_udelay function usable in PBL imported from
> https://github.com/linux4sam/at91bootstrap/blob/v3.8.12/driver/at91_pit.c
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  arch/arm/mach-at91/Makefile                   |  1 +
>  arch/arm/mach-at91/early_udelay.c             | 53 +++++++++++++++++++
>  .../include/mach/at91_lowlevel_clock.h        |  9 ++++
>  .../arm/mach-at91/include/mach/early_udelay.h | 13 +++++
>  4 files changed, 76 insertions(+)
>  create mode 100644 arch/arm/mach-at91/early_udelay.c
>  create mode 100644 arch/arm/mach-at91/include/mach/early_udelay.h
> 
> diff --git a/arch/arm/mach-at91/Makefile b/arch/arm/mach-at91/Makefile
> index 7c4c58b080a1..b8ff6428d05a 100644
> --- a/arch/arm/mach-at91/Makefile
> +++ b/arch/arm/mach-at91/Makefile
> @@ -1,5 +1,6 @@
>  obj-y += setup.o
>  pbl-y += lowlevel_clock.o
> +pbl-$(CONFIG_CLOCKSOURCE_ATMEL_PIT) += early_udelay.o
>  
>  ifeq ($(CONFIG_COMMON_CLK_OF_PROVIDER),)
>  obj-y += clock.o
> diff --git a/arch/arm/mach-at91/early_udelay.c b/arch/arm/mach-at91/early_udelay.c
> new file mode 100644
> index 000000000000..fb8d8bba5434
> --- /dev/null
> +++ b/arch/arm/mach-at91/early_udelay.c
> @@ -0,0 +1,53 @@
> +// SPDX-License-Identifier: BSD-1-Clause
> +/*
> + * Copyright (c) 2012, Atmel Corporation
> + */
> +
> +#include <mach/hardware.h>
> +#include <asm/io.h>
> +#include <mach/at91_lowlevel_clock.h>
> +#include <mach/at91_pit.h>
> +#include <mach/early_udelay.h>
> +
> +static unsigned int master_clock;
> +static void __iomem *pmc, *pit;
> +
> +/* Because the below statement is used in the function:
> + *	((MASTER_CLOCK >> 10) * usec) is used,
> + * to our 32-bit system. the argu "usec" maximum value is:
> + * supposed "MASTER_CLOCK" is 132M.
> + *	132000000 / 1024 = 128906
> + *	(0xffffffff) / 128906 = 33318.
> + * So the maximum delay time is 33318 us.
> + */
> +/* requires PIT to be initialized, but not the clocksource framework */
> +void early_udelay(unsigned int usec)
> +{
> +	unsigned int delay;
> +	unsigned int current;
> +	unsigned int base = readl(pit + AT91_PIT_PIIR);
> +
> +	if (at91_pmc_check_mck_h32mxdiv(pmc))
> +		master_clock /= 2;
> +
> +	delay = ((master_clock >> 10) * usec) >> 14;
> +
> +	do {
> +		current = readl(pit + AT91_PIT_PIIR);
> +		current -= base;
> +	} while (current < delay);
> +}
> +
> +void early_udelay_init(void __iomem *pmc_base,
> +		       void __iomem *pit_base,
> +		       unsigned clock,
> +		       unsigned int master_clock_rate)
> +{
> +	master_clock = master_clock_rate;
> +	pmc = pmc_base;
> +	pit = pit_base;
> +
> +	writel(AT91_PIT_PIV | AT91_PIT_PITEN, pit + AT91_PIT_MR);
> +
> +	at91_pmc_enable_periph_clock(pmc_base, clock);
> +}
> diff --git a/arch/arm/mach-at91/include/mach/at91_lowlevel_clock.h b/arch/arm/mach-at91/include/mach/at91_lowlevel_clock.h
> index 8d04e30b644b..e4bdaade740c 100644
> --- a/arch/arm/mach-at91/include/mach/at91_lowlevel_clock.h
> +++ b/arch/arm/mach-at91/include/mach/at91_lowlevel_clock.h
> @@ -9,6 +9,7 @@
>  #include <errno.h>
>  #include <asm/io.h>
>  #include <mach/at91_pmc.h>
> +#include <linux/types.h>
>  
>  void at91_lowlevel_clock_init(void __iomem *pmc_base);
>  void at91_pmc_cfg_mck(void __iomem *pmc_base, u32 pmc_mckr);
> @@ -40,4 +41,12 @@ static inline int at91_pmc_enable_periph_clock(void __iomem *pmc_base,
>  	return 0;
>  }
>  
> +static inline bool at91_pmc_check_mck_h32mxdiv(void __iomem *pmc_base)
> +{
> +	if (IS_ENABLED(CONFIG_HAVE_AT91_H32MX))
> +		return readl(pmc_base + AT91_PMC_MCKR) & AT91_PMC_H32MXDIV;

Okay, here's another build time dependency on the SoC type. In this case
early_udelay_init() would need a flag whether to apply this additional
divider or not. Even better create SoC specific variants of
early_udelay_init() to make it more convenient for the caller.

Sascha

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