Re: [PATCH v2 16/22] arm64/debug: Make use of the system wide safe value

From: "Suzuki K. Poulose" <Suzuki.Poulose@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com,
	Vladimir.Murzin@arm.com, steve.capper@linaro.org,
	ard.biesheuvel@linaro.org, marc.zyngier@arm.com,
	will.deacon@arm.com, linux-kernel@vger.kernel.org,
	edward.nevill@linaro.org, aph@redhat.com, james.morse@arm.com,
	andre.przywara@arm.com, dave.martin@arm.com
Subject: Re: [PATCH v2 16/22] arm64/debug: Make use of the system wide safe value
Date: Thu, 8 Oct 2015 12:56:28 +0100	[thread overview]
Message-ID: <561659EC.7030508@arm.com> (raw)
In-Reply-To: <20151008111128.GH17192@e104818-lin.cambridge.arm.com>

On 08/10/15 12:11, Catalin Marinas wrote:
> On Mon, Oct 05, 2015 at 06:02:05PM +0100, Suzuki K. Poulose wrote:
>> @@ -137,13 +138,17 @@ extern struct pmu perf_ops_bp;
>>   /* Determine number of BRP registers available. */
>>   static inline int get_num_brps(void)
>>   {
>> -	return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
>> +	return 1 +
>> +		cpuid_feature_extract_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
>> +						ID_AA64DFR0_BRPS_SHIFT);
>>   }
>
> cpuid_feature_extract_field() is fine but we should we bother with
> read_system_reg vs just read_cpuid?
> Similar question for patch 17/22.

Well, we would have already TAINTed the kernel, if these fields are different.
It is just the matter of, whether we want to provide the safer value on a tainted
kernel or not. I am open to suggestions.

Thanks
Suzuki