linux-kernel - Re: [PATCH 05/12] platform/x86: ISST: Add support for MSR 0x54

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Message-ID: <1950741c-b5a9-6883-0c16-391001540a25@redhat.com>
Date:   Wed, 1 Mar 2023 15:30:06 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        markgross@...nel.org
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/12] platform/x86: ISST: Add support for MSR 0x54

Hi,

On 2/11/23 07:32, Srinivas Pandruvada wrote:
> To map Linux CPU numbering scheme to hardware CPU numbering scheme
> MSR 0x53 is getting used. But for new generation of CPUs, this MSR
> is not valid. Since this is model specific MSR, this is possible.
> 
> A new MSR 0x54 is defined. Use this MSR and convert the IOCTL format
> to match existing MSR 0x53, in this case user spaces don't need to
> be aware of this change.
> 
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>

I am not a fan of this. I expect that users of these new CPUs will
very likely also need a new intel-speed-select userspace tool regardless
of doing this MSR munging/shuffling in the kernel. So why not fix
the tool to teach it about the MSR instead ?

If you have good arguments for doing this in the kernel please
add them the commit message for the next version, but my initial
reaction to this is that it is wrong to do this in the kernel
and that the tool should be fixed instead. So my preference
would be for this patch to be dropped from the next version of
the patch-set.

Regards,

Hans







> ---
>  .../intel/speed_select_if/isst_if_common.c    | 51 +++++++++++++++++++
>  1 file changed, 51 insertions(+)
> 
> diff --git a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> index 60e58b0b3835..97d1b4566535 100644
> --- a/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> +++ b/drivers/platform/x86/intel/speed_select_if/isst_if_common.c
> @@ -19,9 +19,13 @@
>  #include <linux/uaccess.h>
>  #include <uapi/linux/isst_if.h>
>  
> +#include <asm/cpu_device_id.h>
> +#include <asm/intel-family.h>
> +
>  #include "isst_if_common.h"
>  
>  #define MSR_THREAD_ID_INFO	0x53
> +#define MSR_PM_LOGICAL_ID	0x54
>  #define MSR_CPU_BUS_NUMBER	0x128
>  
>  static struct isst_if_cmd_cb punit_callbacks[ISST_IF_DEV_MAX];
> @@ -31,6 +35,7 @@ static int punit_msr_white_list[] = {
>  	MSR_CONFIG_TDP_CONTROL,
>  	MSR_TURBO_RATIO_LIMIT1,
>  	MSR_TURBO_RATIO_LIMIT2,
> +	MSR_PM_LOGICAL_ID,
>  };
>  
>  struct isst_valid_cmd_ranges {
> @@ -73,6 +78,8 @@ struct isst_cmd {
>  	u32 param;
>  };
>  
> +static bool isst_hpm_support;
> +
>  static DECLARE_HASHTABLE(isst_hash, 8);
>  static DEFINE_MUTEX(isst_hash_lock);
>  
> @@ -411,11 +418,43 @@ static int isst_if_cpu_online(unsigned int cpu)
>  		isst_cpu_info[cpu].pci_dev[1] = _isst_if_get_pci_dev(cpu, 1, 30, 1);
>  	}
>  
> +	if (isst_hpm_support) {
> +		u64 raw_data;
> +
> +		ret = rdmsrl_safe(MSR_PM_LOGICAL_ID, &raw_data);
> +		if (!ret) {
> +			/*
> +			 * Use the same format as MSR 53, for user space harmony
> +			 *  Format
> +			 *	Bit 0 – thread ID
> +			 *	Bit 8:1 – core ID
> +			 *	Bit 13:9 – Compute domain ID (aka die ID)
> +			 * From the MSR 0x54 format
> +			 *	[15:11] PM_DOMAIN_ID
> +			 *	[10:3] MODULE_ID (aka IDI_AGENT_ID)
> +			 *	[2:0] LP_ID (We don't care about these bits we only
> +			 *			care die and core id
> +			 *	For Atom:
> +			 *		[2] Always 0
> +			 *		[1:0] core ID within module
> +			 *	For Core
> +			 *		[2:1] Always 0
> +			 *		[0] thread ID
> +			 */
> +			data = (raw_data >> 11) & 0x1f;
> +			data <<= 9;
> +			data |= (((raw_data >> 3) & 0xff) << 1);
> +			goto set_punit_id;
> +		}
> +	}
> +
>  	ret = rdmsrl_safe(MSR_THREAD_ID_INFO, &data);
>  	if (ret) {
>  		isst_cpu_info[cpu].punit_cpu_id = -1;
>  		return ret;
>  	}
> +
> +set_punit_id:
>  	isst_cpu_info[cpu].punit_cpu_id = data;
>  
>  	isst_restore_msr_local(cpu);
> @@ -704,6 +743,12 @@ static struct miscdevice isst_if_char_driver = {
>  	.fops		= &isst_if_char_driver_ops,
>  };
>  
> +static const struct x86_cpu_id hpm_cpu_ids[] = {
> +	X86_MATCH_INTEL_FAM6_MODEL(GRANITERAPIDS_X,	NULL),
> +	X86_MATCH_INTEL_FAM6_MODEL(SIERRAFOREST_X,	NULL),
> +	{}
> +};
> +
>  static int isst_misc_reg(void)
>  {
>  	mutex_lock(&punit_misc_dev_reg_lock);
> @@ -711,6 +756,12 @@ static int isst_misc_reg(void)
>  		goto unlock_exit;
>  
>  	if (!misc_usage_count) {
> +		const struct x86_cpu_id *id;
> +
> +		id = x86_match_cpu(hpm_cpu_ids);
> +		if (id)
> +			isst_hpm_support = true;
> +
>  		misc_device_ret = isst_if_cpu_info_init();
>  		if (misc_device_ret)
>  			goto unlock_exit;