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    SubjectRe: [PATCH v2 2/2] soc: mediatek: add a fixed wait for SRAM stable
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    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@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,
    > >>> },
    > >>> };
    > >>>
    > >>>
    > >
    > >


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