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Date:   Sun, 12 Jan 2020 23:44:40 -0800
From:   Ram Pai <linuxram@us.ibm.com>
To:     Pratik Rajesh Sampat <psampat@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
        mpe@ellerman.id.au, svaidy@linux.ibm.com, ego@linux.vnet.ibm.com,
        pratik.sampat@in.ibm.com, pratik.r.sampat@gmail.com
Subject: Re: [RESEND PATCH v2 1/3] powerpc/powernv: Interface to define
 support and preference for a SPR
Reply-To: Ram Pai <linuxram@us.ibm.com>
References: <cover.1578886602.git.psampat@linux.ibm.com>
 <926baad3fd0bf0b01b0adf83c71f2f4f6e9cf1e7.1578886602.git.psampat@linux.ibm.com>
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On Mon, Jan 13, 2020 at 09:15:07AM +0530, Pratik Rajesh Sampat wrote:
> 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>
> ---
>  arch/powerpc/platforms/powernv/idle.c | 327 +++++++++++++++++++++-----
>  1 file changed, 271 insertions(+), 56 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 78599bca66c2..2f328403b0dc 100644
> --- a/arch/powerpc/platforms/powernv/idle.c
> +++ b/arch/powerpc/platforms/powernv/idle.c
> @@ -32,9 +32,106 @@
>  #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;
> +};
> +
> +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,
> +	},

This confuses me.  It says SAVE takes precedence over RESTORE.
and than it says it is strictly 'RESTORE' only.

Maybe you should not initialize the 'supported_mode' ?
or put a comment somewhere here, saying this value will be overwritten
during system initialization?


Otherwise the code looks correct.

Reviewed-by: Ram Pai <linuxram@us.ibm.com>
RP