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Subject: Re: [PATCH v9 3/3] soc: qcom: rpmh: Invoke rpmh_flush() for dirty
 caches
To:     Doug Anderson <dianders@chromium.org>
Cc:     Stephen Boyd <swboyd@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Evan Green <evgreen@chromium.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Andy Gross <agross@kernel.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        Lina Iyer <ilina@codeaurora.org>, lsrao@codeaurora.org
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From:   Maulik Shah <mkshah@codeaurora.org>
Message-ID: <fb50ee6c-b8f9-6685-c4bd-43bcca5a1553@codeaurora.org>
Date:   Tue, 10 Mar 2020 14:41:49 +0530
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On 3/6/2020 3:48 AM, Doug Anderson wrote:
> Hi,
>
> On Thu, Mar 5, 2020 at 1:41 AM Maulik Shah <mkshah@codeaurora.org> wrote:
>  >> There are other cases like below which also gets impacted if driver
>>>> don't cache anything...
>>>>
>>>> for example, when we don’t have dedicated ACTIVE TCS ( if we have below
>>>> config with ACTIVE TCS count 0)
>>>>      qcom,tcs-config = <ACTIVE_TCS  0>,
>>>>                            <SLEEP_TCS   3>,
>>>>                            <WAKE_TCS    3>,
>>>>
>>>> Now to send active data, driver may re-use/ re-purpose few of the sleep
>>>> or wake TCS, to be used as ACTIVE TCS and once work is done,
>>>> it will be re-allocated in SLEEP/ WAKE TCS pool accordingly. If driver
>>>> don’t cache, all the SLEEP and WAKE data is lost when one
>>>> of TCS is repurposed to use as ACTIVE TCS.
>>> Ah, interesting.  I'll read the code more, but are you expecting this
>>> type of situation to work today, or is it theoretical for the future?
>> yes, we have targets which needs to work with this type of situation.
> My brain is still slowly absorbing all the code, but something tells
> me that targets with no ACTIVE TCS will not work properly with non-OSI
> mode unless you change your patches more.  Specifically to make the
> zero ACTIVE TCS case work I think you need a rpmh_flush() call after
> _ALL_ calls to rpmh_write() and rpmh_write_batch() (even those
> modifying ACTIVE state).  rpmh_write_async() will be yet more
> interesting because you'd have to flush in rpmh_tx_done() I guess?
> ...and also somehow you need to inhibit entering sleep mode if an
> async write was in progress?  Maybe easier to just detect the
> "non-OSI-mode + 0 ACTIVE TCS" case at probe time and fail to probe?
>
>
> -Doug
No, it shouldn’t break with "non-OSI-mode + 0 ACTIVE TCS"

After taking your suggestion to do rpmh start/end transaction in v13, rpmh_end_transaction()
invokes rpmh_flush() only for the last client and by this time expecting all of rpmh_write()
and rpmh_write_batch() will be already “finished” as client first waits for them to finish
and then only invokes end.

So driver is good to handle rpmh_write() and rpmh_write_batch() calls.

Regarding rpmh_write_async() call, which is a fire-n-forget request from SW and client driver
may immediately invoke rpmh_end_transaction() after this.

this case is also handled…
Lets again take an example for understanding this..

1.    Client invokes rpmh_write_async() to send ACTIVE cmds for targets which has zero ACTIVE TCS

    Rpmh driver Re-purposes one of SLEEP/WAKE TCS to use as ACTIVE, internally this also sets
    drv->tcs_in_use to true for respective SLEEP/WAKE TCS.

2.    Client now without waiting for above to finish, goes ahead and invokes rpmh_end_transaction()
    which calls rpmh_flush() (in case cache become dirty)

    Now if re-purposed TCS is still in use in HW (transaction in progress), we still have
    drv->tcs_in_use set. So the rpmh_rsc_invalidate() (invoked from rpmh_flush()) will keep on
    returning -EAGAIN until that TCS becomes free to use and then goes ahead to finish its job.
   
Thanks,
Maulik

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