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Date:   Tue, 24 Aug 2021 17:20:42 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Marc Zyngier <maz@kernel.org>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Shier <pshier@google.com>,
        Raghavendra Rao Ananta <rananta@google.com>,
        Ricardo Koller <ricarkol@google.com>,
        Oliver Upton <oupton@google.com>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        kernel-team@android.com
Subject: Re: [PATCH 01/13] clocksource/arm_arch_timer: Drop CNT*_TVAL read
 accessors
Message-ID: <20210824162042.GF96738@C02TD0UTHF1T.local>
References: <20210809152651.2297337-1-maz@kernel.org>
 <20210809152651.2297337-2-maz@kernel.org>
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In-Reply-To: <20210809152651.2297337-2-maz@kernel.org>
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On Mon, Aug 09, 2021 at 04:26:39PM +0100, Marc Zyngier wrote:
> The arch timer driver never reads the various TVAL registers, only
> writes to them. It is thus pointless to provide accessors
> for them and to implement errata workarounds.
> 
> Drop these read-side accessors, and add a couple of BUG() statements
> for the time being. These statements will be removed further down
> the line.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm/include/asm/arch_timer.h    |  6 ++--
>  arch/arm64/include/asm/arch_timer.h  | 17 ++---------
>  drivers/clocksource/arm_arch_timer.c | 44 ++--------------------------
>  3 files changed, 6 insertions(+), 61 deletions(-)
> 
> diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
> index 99175812d903..0c09afaa590d 100644
> --- a/arch/arm/include/asm/arch_timer.h
> +++ b/arch/arm/include/asm/arch_timer.h
> @@ -60,8 +60,7 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
>  			asm volatile("mrc p15, 0, %0, c14, c2, 1" : "=r" (val));
>  			break;
>  		case ARCH_TIMER_REG_TVAL:
> -			asm volatile("mrc p15, 0, %0, c14, c2, 0" : "=r" (val));
> -			break;
> +			BUG();

It would be nice if we had:

	default:
		BUG(); // or maybe BUILD_BUG()

... in all these switches to avoid surprises in future.

If we did that as a prep patch, this patch would be a pure deletion.

Either way, this looks good:

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Builds cleanly, and boots fine on a fast model (both arm/arm64):

Tested-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.

>  		}
>  	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
>  		switch (reg) {
> @@ -69,8 +68,7 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
>  			asm volatile("mrc p15, 0, %0, c14, c3, 1" : "=r" (val));
>  			break;
>  		case ARCH_TIMER_REG_TVAL:
> -			asm volatile("mrc p15, 0, %0, c14, c3, 0" : "=r" (val));
> -			break;
> +			BUG();
>  		}
>  	}
>  
> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h
> index 88d20f04c64a..8e3b2ac60c30 100644
> --- a/arch/arm64/include/asm/arch_timer.h
> +++ b/arch/arm64/include/asm/arch_timer.h
> @@ -52,8 +52,6 @@ struct arch_timer_erratum_workaround {
>  	enum arch_timer_erratum_match_type match_type;
>  	const void *id;
>  	const char *desc;
> -	u32 (*read_cntp_tval_el0)(void);
> -	u32 (*read_cntv_tval_el0)(void);
>  	u64 (*read_cntpct_el0)(void);
>  	u64 (*read_cntvct_el0)(void);
>  	int (*set_next_event_phys)(unsigned long, struct clock_event_device *);
> @@ -64,17 +62,6 @@ struct arch_timer_erratum_workaround {
>  DECLARE_PER_CPU(const struct arch_timer_erratum_workaround *,
>  		timer_unstable_counter_workaround);
>  
> -/* inline sysreg accessors that make erratum_handler() work */
> -static inline notrace u32 arch_timer_read_cntp_tval_el0(void)
> -{
> -	return read_sysreg(cntp_tval_el0);
> -}
> -
> -static inline notrace u32 arch_timer_read_cntv_tval_el0(void)
> -{
> -	return read_sysreg(cntv_tval_el0);
> -}
> -
>  static inline notrace u64 arch_timer_read_cntpct_el0(void)
>  {
>  	return read_sysreg(cntpct_el0);
> @@ -135,14 +122,14 @@ u32 arch_timer_reg_read_cp15(int access, enum arch_timer_reg reg)
>  		case ARCH_TIMER_REG_CTRL:
>  			return read_sysreg(cntp_ctl_el0);
>  		case ARCH_TIMER_REG_TVAL:
> -			return arch_timer_reg_read_stable(cntp_tval_el0);
> +			break;
>  		}
>  	} else if (access == ARCH_TIMER_VIRT_ACCESS) {
>  		switch (reg) {
>  		case ARCH_TIMER_REG_CTRL:
>  			return read_sysreg(cntv_ctl_el0);
>  		case ARCH_TIMER_REG_TVAL:
> -			return arch_timer_reg_read_stable(cntv_tval_el0);
> +			break;
>  		}
>  	}
>  
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index be6d741d404c..9db5c16e31e7 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -141,8 +141,7 @@ u32 arch_timer_reg_read(int access, enum arch_timer_reg reg,
>  			val = readl_relaxed(timer->base + CNTP_CTL);
>  			break;
>  		case ARCH_TIMER_REG_TVAL:
> -			val = readl_relaxed(timer->base + CNTP_TVAL);
> -			break;
> +			BUG();
>  		}
>  	} else if (access == ARCH_TIMER_MEM_VIRT_ACCESS) {
>  		struct arch_timer *timer = to_arch_timer(clk);
> @@ -151,8 +150,7 @@ u32 arch_timer_reg_read(int access, enum arch_timer_reg reg,
>  			val = readl_relaxed(timer->base + CNTV_CTL);
>  			break;
>  		case ARCH_TIMER_REG_TVAL:
> -			val = readl_relaxed(timer->base + CNTV_TVAL);
> -			break;
> +			BUG();
>  		}
>  	} else {
>  		val = arch_timer_reg_read_cp15(access, reg);
> @@ -239,16 +237,6 @@ struct ate_acpi_oem_info {
>  	_new;						\
>  })
>  
> -static u32 notrace fsl_a008585_read_cntp_tval_el0(void)
> -{
> -	return __fsl_a008585_read_reg(cntp_tval_el0);
> -}
> -
> -static u32 notrace fsl_a008585_read_cntv_tval_el0(void)
> -{
> -	return __fsl_a008585_read_reg(cntv_tval_el0);
> -}
> -
>  static u64 notrace fsl_a008585_read_cntpct_el0(void)
>  {
>  	return __fsl_a008585_read_reg(cntpct_el0);
> @@ -285,16 +273,6 @@ static u64 notrace fsl_a008585_read_cntvct_el0(void)
>  	_new;							\
>  })
>  
> -static u32 notrace hisi_161010101_read_cntp_tval_el0(void)
> -{
> -	return __hisi_161010101_read_reg(cntp_tval_el0);
> -}
> -
> -static u32 notrace hisi_161010101_read_cntv_tval_el0(void)
> -{
> -	return __hisi_161010101_read_reg(cntv_tval_el0);
> -}
> -
>  static u64 notrace hisi_161010101_read_cntpct_el0(void)
>  {
>  	return __hisi_161010101_read_reg(cntpct_el0);
> @@ -379,16 +357,6 @@ static u64 notrace sun50i_a64_read_cntvct_el0(void)
>  {
>  	return __sun50i_a64_read_reg(cntvct_el0);
>  }
> -
> -static u32 notrace sun50i_a64_read_cntp_tval_el0(void)
> -{
> -	return read_sysreg(cntp_cval_el0) - sun50i_a64_read_cntpct_el0();
> -}
> -
> -static u32 notrace sun50i_a64_read_cntv_tval_el0(void)
> -{
> -	return read_sysreg(cntv_cval_el0) - sun50i_a64_read_cntvct_el0();
> -}
>  #endif
>  
>  #ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
> @@ -438,8 +406,6 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  		.match_type = ate_match_dt,
>  		.id = "fsl,erratum-a008585",
>  		.desc = "Freescale erratum a005858",
> -		.read_cntp_tval_el0 = fsl_a008585_read_cntp_tval_el0,
> -		.read_cntv_tval_el0 = fsl_a008585_read_cntv_tval_el0,
>  		.read_cntpct_el0 = fsl_a008585_read_cntpct_el0,
>  		.read_cntvct_el0 = fsl_a008585_read_cntvct_el0,
>  		.set_next_event_phys = erratum_set_next_event_tval_phys,
> @@ -451,8 +417,6 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  		.match_type = ate_match_dt,
>  		.id = "hisilicon,erratum-161010101",
>  		.desc = "HiSilicon erratum 161010101",
> -		.read_cntp_tval_el0 = hisi_161010101_read_cntp_tval_el0,
> -		.read_cntv_tval_el0 = hisi_161010101_read_cntv_tval_el0,
>  		.read_cntpct_el0 = hisi_161010101_read_cntpct_el0,
>  		.read_cntvct_el0 = hisi_161010101_read_cntvct_el0,
>  		.set_next_event_phys = erratum_set_next_event_tval_phys,
> @@ -462,8 +426,6 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  		.match_type = ate_match_acpi_oem_info,
>  		.id = hisi_161010101_oem_info,
>  		.desc = "HiSilicon erratum 161010101",
> -		.read_cntp_tval_el0 = hisi_161010101_read_cntp_tval_el0,
> -		.read_cntv_tval_el0 = hisi_161010101_read_cntv_tval_el0,
>  		.read_cntpct_el0 = hisi_161010101_read_cntpct_el0,
>  		.read_cntvct_el0 = hisi_161010101_read_cntvct_el0,
>  		.set_next_event_phys = erratum_set_next_event_tval_phys,
> @@ -484,8 +446,6 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
>  		.match_type = ate_match_dt,
>  		.id = "allwinner,erratum-unknown1",
>  		.desc = "Allwinner erratum UNKNOWN1",
> -		.read_cntp_tval_el0 = sun50i_a64_read_cntp_tval_el0,
> -		.read_cntv_tval_el0 = sun50i_a64_read_cntv_tval_el0,
>  		.read_cntpct_el0 = sun50i_a64_read_cntpct_el0,
>  		.read_cntvct_el0 = sun50i_a64_read_cntvct_el0,
>  		.set_next_event_phys = erratum_set_next_event_tval_phys,
> -- 
> 2.30.2
>