linux-kernel - Re: [PATCH] i2c: designware: Introduce cooldown timer to AMDPSP driver

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Message-ID: <CAOtMz3OR7LspGvXUo-KWNk=1+nYXDAPZy1YV-WtCOL_ihaVyEw@mail.gmail.com>
Date:   Fri, 12 Aug 2022 08:08:28 +0200
From:   Jan Dąbroś <jsd@...ihalf.com>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        andriy.shevchenko@...ux.intel.com, mika.westerberg@...ux.intel.com,
        wsa@...nel.org, rrangel@...omium.org, mw@...ihalf.com,
        upstream@...ihalf.com
Subject: Re: [PATCH] i2c: designware: Introduce cooldown timer to AMDPSP driver

wt., 9 sie 2022 o 14:05 Jarkko Nikula <jarkko.nikula@...ux.intel.com>
napisał(a):
>
> Hi
>
> Sorry the delay, this slipped through my eyes during vacation. Couple
> minor comments below.
>
> On 7/25/22 11:02, Jan Dabros wrote:
> > In order to optimize performance, limit amount of back and forth
> > transactions between x86 and PSP. This is done by introduction of
> > cooldown period - that is window in which x86 isn't releasing the bus
> > immediately after each I2C transaction.
> >
> > In order to protect PSP from being starved while waiting for
> > arbitration, after a programmed time bus is automatically released by a
> > deferred function.
> >
> > Signed-off-by: Jan Dabros <jsd@...ihalf.com>
> > ---
> >   drivers/i2c/busses/i2c-designware-amdpsp.c | 68 +++++++++++++++++-----
> >   1 file changed, 53 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-designware-amdpsp.c b/drivers/i2c/busses/i2c-designware-amdpsp.c
> > index b624356c945f..2e1bb5ae72c3 100644
> > --- a/drivers/i2c/busses/i2c-designware-amdpsp.c
> > +++ b/drivers/i2c/busses/i2c-designware-amdpsp.c
> > @@ -6,6 +6,7 @@
> >   #include <linux/io-64-nonatomic-lo-hi.h>
> >   #include <linux/psp-sev.h>
> >   #include <linux/types.h>
> > +#include <linux/workqueue.h>
> >
> >   #include <asm/msr.h>
> >
> > @@ -15,6 +16,8 @@
> >   #define PSP_MBOX_OFFSET             0x10570
> >   #define PSP_CMD_TIMEOUT_US  (500 * USEC_PER_MSEC)
> >
> > +#define PSP_I2C_COOLDOWN_TIME_MS 100
> > +
>
> "cooldown" distract me thinking thermal management. Would semaphore
> reservation time/timer fit better?

Yes, it makes sense. I will change this here and in the commit message
to "semaphore reservation timer".

>
> > +static void release_bus_now(void)
> > +static void psp_release_i2c_bus_deferred(struct work_struct *work)
> > +static DECLARE_DELAYED_WORK(release_queue, psp_release_i2c_bus_deferred);
> > +
>
> I'd use the same namespace here. Perhaps _now can be dropped from the
> name since the release_bus and release_bus_deferred are near to each
> other and _deferred variant implies it's called after timeout.

Right, release_bus_now -> release_bus.

>
> > +     /*
> > +      * Send a release command to PSP if the cooldown timeout elapsed but x86 still
> > +      * owns the ctrlr.
> > +      */
>
> Replace "ctrlr" -> "control" here since then it doesn't lead to think
> is't some technical object like register etc.

This is about "controller" not "control", but I think your comment is
still applicable.

Best Regards,
Jan