Messages in this thread | | | Subject | Re: [PATCH v2 2/2] soc: mediatek: add a fixed wait for SRAM stable | From | Matthias Brugger <> | Date | Mon, 30 Apr 2018 11:10:28 +0200 |
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On 04/30/2018 09:08 AM, Sean Wang wrote: > 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); > ... >
Is this a performance critical path? I thought if you turn on the power domain for some peripherals, it does not matter if you need a few CPU cycles more or less.
Regards, Matthias
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