Re: [Minios-devel] [UNIKRAFT PATCHv4 35/43] plat/common: Implement CPU suspend for arm64

[Julien Grall <julien.grall@xxxxxxx>]

On 19/07/18 06:54, Wei Chen wrote:
> Hi Julien,
Hi Wei,

> > -----Original Message-----
> > From: Julien Grall <julien.grall@xxxxxxx>
> > Sent: 2018年7月18日 21:28
> > To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx;
> > simon.kuenzer@xxxxxxxxx
> > Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 35/43] plat/common: Implement
> > CPU suspend for arm64
> >
> >
> >
> > On 18/07/18 10:11, Wei Chen wrote:
> > > Hi Julien,
> > Hi Wei,
> >
> > > > -----Original Message-----
> > > > From: Julien Grall <julien.grall@xxxxxxx>
> > > > Sent: 2018年7月16日 21:48
> > > > To: Wei Chen <Wei.Chen@xxxxxxx>; minios-devel@xxxxxxxxxxxxxxxxxxxx;
> > > > simon.kuenzer@xxxxxxxxx
> > > > Cc: Kaly Xin <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> > > > Subject: Re: [Minios-devel] [UNIKRAFT PATCHv4 35/43] plat/common: Implement
> > > > CPU suspend for arm64
> > > >
> > > > Hi Wei,
> > > >
> > > > On 06/07/18 10:03, Wei Chen wrote:
> > > > > Using PSCI despatch function to call PSCI_CPU_SUSPEND
> > > > > function to halt CPU.
> > > > >
> > > > > Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> > > > > ---
> > > > >     plat/common/arm/cpu_native.c        | 44 +++++++++++++++++++++++++++++
> > > > >     plat/common/include/arm/arm64/cpu.h |  2 ++
> > > > >     2 files changed, 46 insertions(+)
> > > > >     create mode 100644 plat/common/arm/cpu_native.c
> > > > >
> > > > > diff --git a/plat/common/arm/cpu_native.c b/plat/common/arm/cpu_native.c
> > > > > new file mode 100644
> > > > > index 0000000..07548bf
> > > > > --- /dev/null
> > > > > +++ b/plat/common/arm/cpu_native.c
> > > > > @@ -0,0 +1,44 @@
> > > > > +/* SPDX-License-Identifier: BSD-3-Clause */
> > > > > +/*
> > > > > + * Authors: Wei Chen <wei.chen@xxxxxxx>
> > > > > + *
> > > > > + * Copyright (c) 2018, Arm Ltd., All rights reserved.
> > > > > + *
> > > > > + * Redistribution and use in source and binary forms, with or without
> > > > > + * modification, are permitted provided that the following conditions
> > > > > + * are met:
> > > > > + *
> > > > > + * 1. Redistributions of source code must retain the above copyright
> > > > > + *    notice, this list of conditions and the following disclaimer.
> > > > > + * 2. Redistributions in binary form must reproduce the above copyright
> > > > > + *    notice, this list of conditions and the following disclaimer in the
> > > > > + *    documentation and/or other materials provided with the distribution.
> > > > > + * 3. Neither the name of the copyright holder nor the names of its
> > > > > + *    contributors may be used to endorse or promote products derived
> > from
> > > > > + *    this software without specific prior written permission.
> > > > > + *
> > > > > + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> > "AS
> > > > IS"
> > > > > + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
> > > > THE
> > > > > + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
> > > > PURPOSE
> > > > > + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
> > > > BE
> > > > > + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
> > > > > + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
> > > > > + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
> > BUSINESS
> > > > > + * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
> > IN
> > > > > + * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
> > > > > + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
> > > > THE
> > > > > + * POSSIBILITY OF SUCH DAMAGE.
> > > > > + *
> > > > > + * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
> > > > > + */
> > > > > +
> > > > > +#include <arm/cpu.h>
> > > > > +#include <arm/cpu_defs.h>
> > > > > +
> > > > > +void halt(void)
> > > > Looking at the usage of halt, I think PSCI CPU suspend is too expensive
> > > > for brief idling.
> > > >
> > > > I am not entirely sure of the semantic expected, but it looks like "wfi"
> > > > would be more suitable here.
> > > Does timer interrupt can wake up wfi? If yes, I think I can't use wfi here.
> > Yes interrupt will wake-up the CPU. This is the same with PSCI suspend.
> >
> > The main difference with the two is the latter will allow you to go in
> > deeper state (depending on the arguments you passed).
> >
> > You don't need that at the moment.
> I checked the code again. Before call halt(), we will call local_disable_irq().
I am not sure why it matters here. From the Arm Arm, the processor will 
leave lower-power mode when receiving an interrupt regardless the value 
of PSTATE.{A, I, F} (See D1.17.2 in ARM DDI 0487C.a).
But not all the callers of halt() will disable the interrupt before (see 
ukplat_lcpu_halt_irq).
Cheers,

--
Julien Grall

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