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Date:   Wed, 18 Mar 2020 20:47:51 +0530
From:   Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
To:     Pratik Rajesh Sampat <psampat@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
        mpe@ellerman.id.au, ego@linux.vnet.ibm.com, linuxram@us.ibm.com,
        psampat@in.ibm.com, pratik.r.sampat@gmail.com
Subject: Re: [PATCH v5 1/3] powerpc/powernv: Interface to define support and
 preference for a SPR
Reply-To: svaidy@linux.ibm.com
References: <20200317141018.42380-1-psampat@linux.ibm.com>
 <20200317141018.42380-2-psampat@linux.ibm.com>
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* Pratik Rajesh Sampat <psampat@linux.ibm.com> [2020-03-17 19:40:16]:

> Define a bitmask interface to determine support for the Self Restore,
> Self Save or both.
> 
> Also define an interface to determine the preference of that SPR to
> be strictly saved or restored or encapsulated with an order of preference.
> 
> The preference bitmask is shown as below:
> ----------------------------
> |... | 2nd pref | 1st pref |
> ----------------------------
> MSB			  LSB
> 
> The preference from higher to lower is from LSB to MSB with a shift of 8
> bits.
> Example:
> Prefer self save first, if not available then prefer self
> restore
> The preference mask for this scenario will be seen as below.
> ((SELF_RESTORE_STRICT << PREFERENCE_SHIFT) | SELF_SAVE_STRICT)
> ---------------------------------
> |... | Self restore | Self save |
> ---------------------------------
> MSB			        LSB
> 
> Finally, declare a list of preferred SPRs which encapsulate the bitmaks
> for preferred and supported with defaults of both being set to support
> legacy firmware.
> 
> This commit also implements using the above interface and retains the
> legacy functionality of self restore.
> 
> Signed-off-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
> Reviewed-by: Ram Pai <linuxram@us.ibm.com>

Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>


> ---
>  arch/powerpc/platforms/powernv/idle.c | 316 +++++++++++++++++++++-----
>  1 file changed, 259 insertions(+), 57 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 78599bca66c2..03fe835aadd1 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -32,9 +32,112 @@
>  #define P9_STOP_SPR_MSR 2000
>  #define P9_STOP_SPR_PSSCR      855
>  
> +/* Interface for the stop state supported and preference */
> +#define SELF_RESTORE_TYPE    0
> +#define SELF_SAVE_TYPE       1
> +
> +#define NR_PREFERENCES    2
> +#define PREFERENCE_SHIFT  4
> +#define PREFERENCE_MASK   0xf
> +
> +#define UNSUPPORTED         0x0
> +#define SELF_RESTORE_STRICT 0x1
> +#define SELF_SAVE_STRICT    0x2
> +
> +/*
> + * Bitmask defining the kind of preferences available.
> + * Note : The higher to lower preference is from LSB to MSB, with a shift of
> + * 4 bits.
> + * ----------------------------
> + * |    | 2nd pref | 1st pref |
> + * ----------------------------
> + * MSB			      LSB
> + */
> +/* Prefer Restore if available, otherwise unsupported */
> +#define PREFER_SELF_RESTORE_ONLY	SELF_RESTORE_STRICT
> +/* Prefer Save if available, otherwise unsupported */
> +#define PREFER_SELF_SAVE_ONLY		SELF_SAVE_STRICT
> +/* Prefer Restore when available, otherwise prefer Save */
> +#define PREFER_RESTORE_SAVE		((SELF_SAVE_STRICT << \
> +					  PREFERENCE_SHIFT)\
> +					  | SELF_RESTORE_STRICT)
> +/* Prefer Save when available, otherwise prefer Restore*/
> +#define PREFER_SAVE_RESTORE		((SELF_RESTORE_STRICT <<\
> +					  PREFERENCE_SHIFT)\
> +					  | SELF_SAVE_STRICT)
>  static u32 supported_cpuidle_states;
>  struct pnv_idle_states_t *pnv_idle_states;
>  int nr_pnv_idle_states;
> +/* Caching the lpcr & ptcr support to use later */
> +static bool is_lpcr_self_save;
> +static bool is_ptcr_self_save;
> +
> +struct preferred_sprs {
> +	u64 spr;
> +	u32 preferred_mode;
> +	u32 supported_mode;
> +};
> +
> +/*
> + * Preferred mode: Order of precedence when both self-save and self-restore
> + *		   supported
> + * Supported mode: Default support. Can be overwritten during system
> + *		   initialization
> + */
> +struct preferred_sprs preferred_sprs[] = {
> +	{
> +		.spr = SPRN_HSPRG0,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_LPCR,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_PTCR,
> +		.preferred_mode = PREFER_SAVE_RESTORE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_HMEER,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_HID0,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = P9_STOP_SPR_MSR,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = P9_STOP_SPR_PSSCR,
> +		.preferred_mode = PREFER_SAVE_RESTORE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_HID1,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_HID4,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	},
> +	{
> +		.spr = SPRN_HID5,
> +		.preferred_mode = PREFER_RESTORE_SAVE,
> +		.supported_mode = SELF_RESTORE_STRICT,
> +	}
> +};
> +
> +const int nr_preferred_sprs = ARRAY_SIZE(preferred_sprs);
>  
>  /*
>   * The default stop state that will be used by ppc_md.power_save
> @@ -61,78 +164,170 @@ static bool deepest_stop_found;
>  
>  static unsigned long power7_offline_type;
>  
> -static int pnv_save_sprs_for_deep_states(void)
> +static int pnv_self_restore_sprs(u64 pir, int cpu, u64 spr)
>  {
> -	int cpu;
> +	u64 reg_val;
>  	int rc;
>  
> -	/*
> -	 * hid0, hid1, hid4, hid5, hmeer and lpcr values are symmetric across
> -	 * all cpus at boot. Get these reg values of current cpu and use the
> -	 * same across all cpus.
> -	 */
> -	uint64_t lpcr_val	= mfspr(SPRN_LPCR);
> -	uint64_t hid0_val	= mfspr(SPRN_HID0);
> -	uint64_t hid1_val	= mfspr(SPRN_HID1);
> -	uint64_t hid4_val	= mfspr(SPRN_HID4);
> -	uint64_t hid5_val	= mfspr(SPRN_HID5);
> -	uint64_t hmeer_val	= mfspr(SPRN_HMEER);
> -	uint64_t msr_val = MSR_IDLE;
> -	uint64_t psscr_val = pnv_deepest_stop_psscr_val;
> -
> -	for_each_present_cpu(cpu) {
> -		uint64_t pir = get_hard_smp_processor_id(cpu);
> -		uint64_t hsprg0_val = (uint64_t)paca_ptrs[cpu];
> -
> -		rc = opal_slw_set_reg(pir, SPRN_HSPRG0, hsprg0_val);
> +	switch (spr) {
> +	case SPRN_HSPRG0:
> +		reg_val = (uint64_t)paca_ptrs[cpu];
> +		rc = opal_slw_set_reg(pir, SPRN_HSPRG0, reg_val);
>  		if (rc != 0)
>  			return rc;
> -
> -		rc = opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
> +		break;
> +	case SPRN_LPCR:
> +		reg_val = mfspr(SPRN_LPCR);
> +		rc = opal_slw_set_reg(pir, SPRN_LPCR, reg_val);
>  		if (rc != 0)
>  			return rc;
> -
> +		break;
> +	case P9_STOP_SPR_MSR:
> +		reg_val = MSR_IDLE;
>  		if (cpu_has_feature(CPU_FTR_ARCH_300)) {
> -			rc = opal_slw_set_reg(pir, P9_STOP_SPR_MSR, msr_val);
> +			rc = opal_slw_set_reg(pir, P9_STOP_SPR_MSR, reg_val);
>  			if (rc)
>  				return rc;
> -
> -			rc = opal_slw_set_reg(pir,
> -					      P9_STOP_SPR_PSSCR, psscr_val);
> -
> +		}
> +		break;
> +	case P9_STOP_SPR_PSSCR:
> +		reg_val = pnv_deepest_stop_psscr_val;
> +		if (cpu_has_feature(CPU_FTR_ARCH_300)) {
> +			rc = opal_slw_set_reg(pir, P9_STOP_SPR_PSSCR, reg_val);
>  			if (rc)
>  				return rc;
>  		}
> -
> -		/* HIDs are per core registers */
> +		break;
> +	case SPRN_HMEER:
> +		reg_val = mfspr(SPRN_HMEER);
>  		if (cpu_thread_in_core(cpu) == 0) {
> -
> -			rc = opal_slw_set_reg(pir, SPRN_HMEER, hmeer_val);
> -			if (rc != 0)
> +			rc = opal_slw_set_reg(pir, SPRN_HMEER, reg_val);
> +			if (rc)
>  				return rc;
> -
> -			rc = opal_slw_set_reg(pir, SPRN_HID0, hid0_val);
> -			if (rc != 0)
> +		}
> +		break;
> +	case SPRN_HID0:
> +		reg_val = mfspr(SPRN_HID0);
> +		if (cpu_thread_in_core(cpu) == 0) {
> +			rc = opal_slw_set_reg(pir, SPRN_HID0, reg_val);
> +			if (rc)
>  				return rc;
> +		}
> +		break;
> +	case SPRN_HID1:
> +		reg_val = mfspr(SPRN_HID1);
> +		if (cpu_thread_in_core(cpu) == 0 &&
> +		    !cpu_has_feature(CPU_FTR_ARCH_300)) {
> +			rc = opal_slw_set_reg(pir, SPRN_HID1, reg_val);
> +			if (rc)
> +				return rc;
> +		}
> +		break;
> +	case SPRN_HID4:
> +		reg_val = mfspr(SPRN_HID4);
> +		if (cpu_thread_in_core(cpu) == 0 &&
> +		    !cpu_has_feature(CPU_FTR_ARCH_300)) {
> +			rc = opal_slw_set_reg(pir, SPRN_HID4, reg_val);
> +			if (rc)
> +				return rc;
> +		}
> +		break;
> +	case SPRN_HID5:
> +		reg_val = mfspr(SPRN_HID5);
> +		if (cpu_thread_in_core(cpu) == 0 &&
> +		    !cpu_has_feature(CPU_FTR_ARCH_300)) {
> +			rc = opal_slw_set_reg(pir, SPRN_HID5, reg_val);
> +			if (rc)
> +				return rc;
> +		}
> +		break;
> +	case SPRN_PTCR:
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +	return 0;
> +}
>  
> -			/* Only p8 needs to set extra HID regiters */
> -			if (!cpu_has_feature(CPU_FTR_ARCH_300)) {
> -
> -				rc = opal_slw_set_reg(pir, SPRN_HID1, hid1_val);
> -				if (rc != 0)
> -					return rc;
> -
> -				rc = opal_slw_set_reg(pir, SPRN_HID4, hid4_val);
> -				if (rc != 0)
> -					return rc;
> -
> -				rc = opal_slw_set_reg(pir, SPRN_HID5, hid5_val);
> -				if (rc != 0)
> -					return rc;
> +static int pnv_self_save_restore_sprs(void)
> +{
> +	int rc, index, cpu, k;
> +	u64 pir;
> +	struct preferred_sprs curr_spr;
> +	bool is_initialized;
> +	u32 preferred;
> +
> +	is_lpcr_self_save = false;
> +	is_ptcr_self_save = false;
> +	for_each_present_cpu(cpu) {
> +		pir = get_hard_smp_processor_id(cpu);
> +		for (index = 0; index < nr_preferred_sprs; index++) {
> +			curr_spr = preferred_sprs[index];
> +			is_initialized = false;
> +			/*
> +			 * Go through each of the preferences
> +			 * Check if it is preferred as well as supported
> +			 */
> +			for (k = 0; k < NR_PREFERENCES; k++) {
> +				preferred = curr_spr.preferred_mode
> +						& PREFERENCE_MASK;
> +				if (preferred & curr_spr.supported_mode
> +				    & SELF_RESTORE_STRICT) {
> +					is_initialized = true;
> +					rc = pnv_self_restore_sprs(pir, cpu,
> +								curr_spr.spr);
> +					if (rc != 0)
> +						return rc;
> +					break;
> +				}
> +				preferred_sprs[index].preferred_mode =
> +					preferred_sprs[index].preferred_mode >>
> +					PREFERENCE_SHIFT;
> +				curr_spr = preferred_sprs[index];
> +			}
> +			if (!is_initialized) {
> +				if (preferred_sprs[index].spr == SPRN_PTCR ||
> +				    (cpu_has_feature(CPU_FTR_ARCH_300) &&
> +				    (preferred_sprs[index].spr == SPRN_HID1 ||
> +				     preferred_sprs[index].spr == SPRN_HID4 ||
> +				     preferred_sprs[index].spr == SPRN_HID5)))
> +					continue;
> +				return OPAL_UNSUPPORTED;
>  			}
>  		}
>  	}
> +	return 0;
> +}
>  
> +static int pnv_save_sprs_for_deep_states(void)
> +{
> +	int rc;
> +	int index;
> +
> +	/*
> +	 * Iterate over the preffered SPRs and if even one of them is
> +	 * still unsupported We cut support for deep stop states
> +	 */
> +	for (index = 0; index < nr_preferred_sprs; index++) {
> +		if (preferred_sprs[index].supported_mode == UNSUPPORTED) {
> +			if (preferred_sprs[index].spr == SPRN_PTCR ||
> +			    (cpu_has_feature(CPU_FTR_ARCH_300) &&
> +			    (preferred_sprs[index].spr == SPRN_HID1 ||
> +			     preferred_sprs[index].spr == SPRN_HID4 ||
> +			     preferred_sprs[index].spr == SPRN_HID5)))
> +				continue;
> +			return OPAL_UNSUPPORTED;
> +		}
> +	}
> +	/*
> +	 * Try to self-restore the registers that can be self restored if self
> +	 * restore is active, try the same for the registers that
> +	 * can be self saved too.
> +	 * Note : If both are supported, self restore is given more priority
> +	 */
> +	rc = pnv_self_save_restore_sprs();
> +	if (rc != 0)
> +		return rc;
>  	return 0;
>  }
>  
> @@ -658,7 +853,8 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  		mmcr0		= mfspr(SPRN_MMCR0);
>  	}
>  	if ((psscr & PSSCR_RL_MASK) >= pnv_first_spr_loss_level) {
> -		sprs.lpcr	= mfspr(SPRN_LPCR);
> +		if (!is_lpcr_self_save)
> +			sprs.lpcr	= mfspr(SPRN_LPCR);
>  		sprs.hfscr	= mfspr(SPRN_HFSCR);
>  		sprs.fscr	= mfspr(SPRN_FSCR);
>  		sprs.pid	= mfspr(SPRN_PID);
> @@ -672,7 +868,8 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  		sprs.mmcr1	= mfspr(SPRN_MMCR1);
>  		sprs.mmcr2	= mfspr(SPRN_MMCR2);
>  
> -		sprs.ptcr	= mfspr(SPRN_PTCR);
> +		if (!is_ptcr_self_save)
> +			sprs.ptcr	= mfspr(SPRN_PTCR);
>  		sprs.rpr	= mfspr(SPRN_RPR);
>  		sprs.tscr	= mfspr(SPRN_TSCR);
>  		if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
> @@ -756,7 +953,8 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  		goto core_woken;
>  
>  	/* Per-core SPRs */
> -	mtspr(SPRN_PTCR,	sprs.ptcr);
> +	if (!is_ptcr_self_save)
> +		mtspr(SPRN_PTCR,	sprs.ptcr);
>  	mtspr(SPRN_RPR,		sprs.rpr);
>  	mtspr(SPRN_TSCR,	sprs.tscr);
>  
> @@ -777,7 +975,8 @@ static unsigned long power9_idle_stop(unsigned long psscr, bool mmu_on)
>  	atomic_unlock_and_stop_thread_idle();
>  
>  	/* Per-thread SPRs */
> -	mtspr(SPRN_LPCR,	sprs.lpcr);
> +	if (!is_lpcr_self_save)
> +		mtspr(SPRN_LPCR,	sprs.lpcr);
>  	mtspr(SPRN_HFSCR,	sprs.hfscr);
>  	mtspr(SPRN_FSCR,	sprs.fscr);
>  	mtspr(SPRN_PID,		sprs.pid);
> @@ -956,8 +1155,11 @@ void pnv_program_cpu_hotplug_lpcr(unsigned int cpu, u64 lpcr_val)
>  	 * Program the LPCR via stop-api only if the deepest stop state
>  	 * can lose hypervisor context.
>  	 */
> -	if (supported_cpuidle_states & OPAL_PM_LOSE_FULL_CONTEXT)
> -		opal_slw_set_reg(pir, SPRN_LPCR, lpcr_val);
> +	if (supported_cpuidle_states & OPAL_PM_LOSE_FULL_CONTEXT) {
> +		if (!is_lpcr_self_save)
> +			opal_slw_set_reg(pir, SPRN_LPCR,
> +					 lpcr_val);
> +	}
>  }
>  
>  /*

This framework provides a flexible interface to exploit microcode
capabilities to save and restore and SPR.  The complexity in the
implementation and the various options are mainly to provide backward
compatibility to OPAL and Linux on top of different microcode
capabilities and platforms.

--Vaidy