[PATCH v2 2/2] soc: mediatek: add a fixed wait for SRAM stable

Sean Wang
2018-04-30T07:08:00Z

On Fri, 2018-04-27 at 11:46 +0200, Matthias Brugger wrote:
> Hi Sean,
>
> On 04/23/2018 11:39 AM, Sean Wang wrote:
> > On Mon, 2018-04-23 at 11:31 +0200, Matthias Brugger wrote:
> >>
> >> On 04/23/2018 10:36 AM, sean.wang at mediatek.com wrote:
> >>> From: Sean Wang <sean.wang@mediatek.com>
> >>>
> >>> MT7622_POWER_DOMAIN_WB doesn't send an ACK when its managed SRAM becomes
> >>> stable, which is not like the behavior the other power domains should
> >>> have. Therefore, it's necessary for such a power domain to have a fixed
> >>> and well-predefined duration to wait until its managed SRAM can be allowed
> >>> to access by all functions running on the top.
> >>>
> >>> v1 -> v2:
> >>> - use MTK_SCPD_FWAIT_SRAM flag as an indication requiring force waiting.
> >>>
> >>> Signed-off-by: Sean Wang <sean.wang@mediatek.com>
> >>> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> >>> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> >>> Cc: Weiyi Lu <weiyi.lu@mediatek.com>
> >>> ---
> >>> drivers/soc/mediatek/mtk-scpsys.c | 24 ++++++++++++++++++------
> >>> 1 file changed, 18 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/drivers/soc/mediatek/mtk-scpsys.c b/drivers/soc/mediatek/mtk-scpsys.c
> >>> index b1b45e4..d4f1a63 100644
> >>> --- a/drivers/soc/mediatek/mtk-scpsys.c
> >>> +++ b/drivers/soc/mediatek/mtk-scpsys.c
> >>> @@ -32,6 +32,7 @@
> >>> #define MTK_POLL_TIMEOUT (jiffies_to_usecs(HZ))
> >>>
> >>> #define MTK_SCPD_ACTIVE_WAKEUP BIT(0)
> >>> +#define MTK_SCPD_FWAIT_SRAM BIT(1)
> >>> #define MTK_SCPD_CAPS(_scpd, _x) ((_scpd)->data->caps & (_x))
> >>>
> >>> #define SPM_VDE_PWR_CON 0x0210
> >>> @@ -237,11 +238,22 @@ static int scpsys_power_on(struct generic_pm_domain *genpd)
> >>> val &= ~scpd->data->sram_pdn_bits;
> >>> writel(val, ctl_addr);
> >>>
> >>> - /* wait until SRAM_PDN_ACK all 0 */
> >>> - ret = readl_poll_timeout(ctl_addr, tmp, (tmp & pdn_ack) == 0,
> >>> - MTK_POLL_DELAY_US, MTK_POLL_TIMEOUT);
> >>> - if (ret < 0)
> >>> - goto err_pwr_ack;
> >>> + /* Either wait until SRAM_PDN_ACK all 0 or have a force wait */
> >>> + if (!MTK_SCPD_CAPS(scpd, MTK_SCPD_FWAIT_SRAM)) {
>
> After having another look on the patch, could you change the order of the if:
> So that we check for the existence of the MTK_SCPD_FWAIT_SRAM and sleep and in
> the else branch we to the readl_poll_timeout.
>
> I think in the future this will make the code easier to understand as you can
> easily oversee the '!' negation in the if.
>
> Regards,
> Matthias
>

Initial thought on the patch is that I would like to save a branch
instruction for a most possibly executed block. Or would it be better to
add a compiler to branch prediction information? something like that

/* Either wait until SRAM_PDN_ACK all 0 or have a force wait */
if (unlikely(MTK_SCPD_CAPS(scpd, MTK_SCPD_FWAIT_SRAM))) {
/*
* Currently, MTK_SCPD_FWAIT_SRAM is necessary only for
* MT7622_POWER_DOMAIN_WB and thus just a trivial setup
is
* applied here.
*/
usleep_range(12000, 12100);
...

>
> >>> + ret = readl_poll_timeout(ctl_addr, tmp, (tmp & pdn_ack) == 0,
> >>> + MTK_POLL_DELAY_US, MTK_POLL_TIMEOUT);
> >>> + if (ret < 0)
> >>> + goto err_pwr_ack;
> >>> + } else {
> >>> + /*
> >>> + * Currently, MTK_SCPD_FWAIT_SRAM is necessary only for
> >>> + * MT7622_POWER_DOMAIN_WB and thus just a trivial setup is
> >>> + * applied here. If there're more domains which need to force
> >>> + * waiting for its own pre-defined value, the duration should
> >>> + * be coded in the caps field.
> >>> + */
> >>
> >> I would say, if necessary in the future we can add a switch statement here.
> >> Other then that the patches look good. If you are OK, I'll just delete the last
> >> sentence when applying the patch.
> >>
> >
> > yes, it's okay for me.
> >
> >> Regards,
> >> Matthias
> >>
> >>> + usleep_range(12000, 12100);
> >>> + };
> >>>
> >>> if (scpd->data->bus_prot_mask) {
> >>> ret = mtk_infracfg_clear_bus_protection(scp->infracfg,
> >>> @@ -785,7 +797,7 @@ static const struct scp_domain_data scp_domain_data_mt7622[] = {
> >>> .sram_pdn_ack_bits = 0,
> >>> .clk_id = {CLK_NONE},
> >>> .bus_prot_mask = MT7622_TOP_AXI_PROT_EN_WB,
> >>> - .caps = MTK_SCPD_ACTIVE_WAKEUP,
> >>> + .caps = MTK_SCPD_ACTIVE_WAKEUP | MTK_SCPD_FWAIT_SRAM,
> >>> },
> >>> };
> >>>
> >>>
> >
> >