From: Sean Wang <sean.wang@mediatek.com>
To: Matthias Brugger <matthias.bgg@gmail.com>
Cc: <rjw@rjwysocki.net>, <khilman@baylibre.com>,
<ulf.hansson@linaro.org>, <linux-mediatek@lists.infradead.org>,
<linux-pm@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>,
"Weiyi Lu" <weiyi.lu@mediatek.com>
Subject: Re: [PATCH v2 2/2] soc: mediatek: add a fixed wait for SRAM stable
Date: Mon, 30 Apr 2018 17:59:11 +0800 [thread overview]
Message-ID: <1525082351.12322.230.camel@mtkswgap22> (raw)
In-Reply-To: <b45efd5d-755c-6d5c-b226-763801e811ea@gmail.com>
On Mon, 2018-04-30 at 11:10 +0200, Matthias Brugger wrote:
>
> 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.
thanks for your advice
it's not a critical path.
i'll send a new patch according to the result.
> Regards,
> Matthias
next prev parent reply other threads:[~2018-04-30 9:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-23 8:36 [PATCH v2 1/2] soc: mediatek: introduce a CAPS flag for scp_domain_data sean.wang
2018-04-23 8:36 ` [PATCH v2 2/2] soc: mediatek: add a fixed wait for SRAM stable sean.wang
2018-04-23 9:31 ` Matthias Brugger
2018-04-23 9:39 ` Sean Wang
2018-04-27 9:46 ` Matthias Brugger
2018-04-30 7:08 ` Sean Wang
2018-04-30 9:10 ` Matthias Brugger
2018-04-30 9:59 ` Sean Wang [this message]
2018-04-27 9:43 ` [PATCH v2 1/2] soc: mediatek: introduce a CAPS flag for scp_domain_data Matthias Brugger
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