linux-kernel - Re: [RFC 1/3] powerpc/powernv: Interface to define support and preference for a SPR

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Message-Id: <20200103232457.GH5556@oc0525413822.ibm.com>
Date:   Fri, 3 Jan 2020 15:24:57 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     Pratik Rajesh Sampat <psampat@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
        mpe@...erman.id.au, svaidy@...ux.ibm.com, ego@...ux.vnet.ibm.com,
        pratik.sampat@...ibm.com
Subject: Re: [RFC 1/3] powerpc/powernv: Interface to define support and
 preference for a SPR

On Wed, Dec 04, 2019 at 03:02:53PM +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@...ux.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/idle.c | 325 +++++++++++++++++++++-----
>  1 file changed, 269 insertions(+), 56 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> index 78599bca66c2..d38b8b6dcbce 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  8
> +#define PREFERENCE_MASK   0xff
> +
> +#define UNSUPPORTED         0x0
> +#define SELF_RESTORE_STRICT 0x01
> +#define SELF_SAVE_STRICT    0x10
> +
> +/*
> + * Bitmask defining the kind of preferences available.
> + * Note : The higher to lower preference is from LSB to MSB, with a shift of
> + * 8 bits.

A minor comment.

Is there a reason why shift is 8?  Shift of 4 must be sufficient,
and a mask of '0xf' should do. And SELF_SAVE_STRICT can be 0x2.



> + * ----------------------------
> + * |    | 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;

I understand why you need to track the status of PTCR register.
But its not clear, why LPCR register's save status need to be tracked?


> +
> +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,
> +	},
> +	{
> +		.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,
> +	}
> +};

What determines the list of registers tracked in this table?


.snip..

-- 
Ram Pai