linux-kernel - Re: [PATCH 2/2] firmware: arm_scmi: mark channel free when init

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Date:   Fri, 7 Feb 2020 10:40:43 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH 2/2] firmware: arm_scmi: mark channel free when init

On Fri, Feb 07, 2020 at 02:16:04AM +0000, Peng Fan wrote:
>
> > Subject: Re: [PATCH 2/2] firmware: arm_scmi: mark channel free when init
> >
> > On Thu, Feb 06, 2020 at 08:57:26PM +0800, peng.fan@....com wrote:
> > > From: Peng Fan <peng.fan@....com>
> > >
> > > The firmware itself might not mark channel free, so let's explicitly
> > > mark it free when do initialization.
> > >
> > > Also move struct scmi_shared_mem to common.h
> > >
> > > Signed-off-by: Peng Fan <peng.fan@....com>
> > > ---
> > >  drivers/firmware/arm_scmi/common.h  | 19 +++++++++++++++++--
> > > drivers/firmware/arm_scmi/mailbox.c |  2 ++
> > >  drivers/firmware/arm_scmi/shmem.c   | 18 ------------------
> > >  3 files changed, 19 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/drivers/firmware/arm_scmi/common.h
> > > b/drivers/firmware/arm_scmi/common.h
> > > index fd091a4ccbff..5df262a564a4 100644
> > > --- a/drivers/firmware/arm_scmi/common.h
> > > +++ b/drivers/firmware/arm_scmi/common.h
> > > @@ -211,8 +211,23 @@ extern const struct scmi_desc scmi_mailbox_desc;
> > > void scmi_rx_callback(struct scmi_chan_info *cinfo, u32 msg_hdr);
> > > void scmi_free_channel(struct scmi_chan_info *cinfo, struct idr *idr,
> > > int id);
> > >
> > > -/* shmem related declarations */
> > > -struct scmi_shared_mem;
> > > +/*
> > > + * SCMI specification requires all parameters, message headers,
> > > +return
> > > + * arguments or any protocol data to be expressed in little endian
> > > + * format only.
> > > + */
> > > +struct scmi_shared_mem {
> > > +	__le32 reserved;
> > > +	__le32 channel_status;
> > > +#define SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR	BIT(1)
> > > +#define SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE	BIT(0)
> > > +	__le32 reserved1[2];
> > > +	__le32 flags;
> > > +#define SCMI_SHMEM_FLAG_INTR_ENABLED	BIT(0)
> > > +	__le32 length;
> > > +	__le32 msg_header;
> > > +	u8 msg_payload[0];
> > > +};
> > >
> > >  void shmem_tx_prepare(struct scmi_shared_mem __iomem *shmem,
> > >  		      struct scmi_xfer *xfer);
> > > diff --git a/drivers/firmware/arm_scmi/mailbox.c
> > > b/drivers/firmware/arm_scmi/mailbox.c
> > > index 68ed58e2a47a..2d34bf6e94e2 100644
> > > --- a/drivers/firmware/arm_scmi/mailbox.c
> > > +++ b/drivers/firmware/arm_scmi/mailbox.c
> > > @@ -104,6 +104,8 @@ static int mailbox_chan_setup(struct
> > scmi_chan_info *cinfo, struct device *dev,
> > >  	cinfo->transport_info = smbox;
> > >  	smbox->cinfo = cinfo;
> > >
> > > +	iowrite32(BIT(0), &smbox->shmem->channel_status);
> > > +
> >
>
> +arm list
>
> > If we need this then we may need to put this as a function in shmem.c I am
> > still not convinced if we can do this unconditionally, i.e. will that affect Rx
> > channel if there's notification pending before we initialise. But we can deal
> > with that later.
>
> Per understanding, channel is specific to an agent, it could not be shared.
> So the shmem binded to the channel will not be used by others.
>

Yes

> Since this is the initialization process, the firmware might not init the shmem.
>

But, is there any particular reason for firmware not to ? It means platform
holds the channel and needs to release it to agent(OSPM) in this case after
initialisation.

> The shmem.c shmem_tx_prepare will spin until channel free, so I did the patch.
> Otherwise it might spin forever.
>

Yes I guessed that to be reason.

> I'll add a check as following
> if (tx)
>  iowrite32(BIT(0), &smbox->shmem->channel_status);
>

Not yet, I need answers to above query.

> I not find a good place to put this in shmem.c (:
>

Least of the problem :), let us first agree if we have to have it.

> >
> > Also what about error fields ? I would rather clear it to 0, not just BIT(0)
>
> Tx channel error should also be cleared, fix in v2.
>

OK but wait for a while before you post for the discussion to end.

--
Regards,
Sudeep