linux-kernel - Re: [PATCH v1 2/2] firmware: arm_scmi: Augment SMC/HVC to allow optional interrupt

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Date:   Wed, 11 Nov 2020 17:45:46 +0000
From:   Cristian Marussi <cristian.marussi@....com>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] firmware: arm_scmi: Augment SMC/HVC to allow
 optional interrupt

On Wed, Nov 11, 2020 at 11:45:24AM -0500, Jim Quinlan wrote:
> On Wed, Nov 11, 2020 at 5:42 AM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > On Tue, Nov 10, 2020 at 01:38:19PM -0500, Jim Quinlan wrote:
> > > The SMC/HVC SCMI transport is modified to allow the completion of an SCMI
> > > message to be indicated by an interrupt rather than the return of the smc
> > > call.  This accommodates the existing behavior of the BrcmSTB SCMI
> > > "platform" whose SW is already out in the field and cannot be changed.
> > >
> > > Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
> > > ---
> > >  drivers/firmware/arm_scmi/smc.c | 31 +++++++++++++++++++++++++++++++
> > >  1 file changed, 31 insertions(+)
> > >
> > > diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
> > > index 82a82a5dc86a..3bf935dbd00e 100644
> > > --- a/drivers/firmware/arm_scmi/smc.c
> > > +++ b/drivers/firmware/arm_scmi/smc.c
> > > @@ -9,9 +9,11 @@
> > >  #include <linux/arm-smccc.h>
> > >  #include <linux/device.h>
> > >  #include <linux/err.h>
> > > +#include <linux/interrupt.h>
> > >  #include <linux/mutex.h>
> > >  #include <linux/of.h>
> > >  #include <linux/of_address.h>
> > > +#include <linux/of_irq.h>
> > >  #include <linux/slab.h>
> > >
> > >  #include "common.h"
> > > @@ -23,6 +25,8 @@
> > >   * @shmem: Transmit/Receive shared memory area
> > >   * @shmem_lock: Lock to protect access to Tx/Rx shared memory area
> > >   * @func_id: smc/hvc call function id
> > > + * @irq: Optional; employed when platforms indicates msg completion by intr.
> > > + * @tx_complete: Optional, employed only when irq is valid.
> > >   */
> > >
> > >  struct scmi_smc {
> > > @@ -30,8 +34,19 @@ struct scmi_smc {
> > >       struct scmi_shared_mem __iomem *shmem;
> > >       struct mutex shmem_lock;
> > >       u32 func_id;
> > > +     int irq;
> > > +     struct completion tx_complete;
> > >  };
> > >
> > > +static irqreturn_t smc_msg_done_isr(int irq, void *data)
> > > +{
> > > +     struct scmi_smc *scmi_info = data;
> > > +
> > > +     complete(&scmi_info->tx_complete);
> > > +
> > > +     return IRQ_HANDLED;
> > > +}
> > > +
> > >  static bool smc_chan_available(struct device *dev, int idx)
> > >  {
> > >       struct device_node *np = of_parse_phandle(dev->of_node, "shmem", 0);
> > > @@ -79,6 +94,20 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> > >       if (ret < 0)
> > >               return ret;
> > >
> > > +     /* Optional feature -- signal message completion using an interrupt */
> > > +     ret = of_irq_get_byname(cdev->of_node, "msg-serviced");
> >
> > So, looks like it is mandatory if "interrupts" is used. Please update the
> > binding or if that is not the practice followed elsewhere, drop search by
> > name.
> 
> Well, I can certainly change the comment. I do not want it to be
> "mandatory" if just interrupts are used.
>  The reason I prefer using "interrupt-names" is that this allows
> unforeseen use of future additional interrupts w/o caring about order
> in the interrupts DT node.  If you are absolutely positive that there
> will never be other interrupts used  in the future for the SCMI node
> then I will drop it.
> 

What about the future possibility of adding p2a notifications handling
to SMC transport, won't that need some other IRQ (and shmem) ?

Regards

Cristian

> >
> > Also I prefer full name "message-serviced" if possible, not strong
> > opinion.
> 
> Will do.
> 
> >
> >
> > > +     if (ret > 0) {
> > > +             scmi_info->irq = ret;
> >
> > May be set this only if we succeed setting up handler ? I mean move this
> > down.
> 
> Will do.
> 
> Regards,
> Jim Quinlan
> Broadcom STB
> 
> 
> >
> >
> > Other than these, the changes look fine.
> >
> > --
> > Regards,
> > Sudeep