RE: [PATCH 2/2] firmware: arm_scmi: mark channel free when init

[Peng Fan]

> 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@xxxxxxx wrote:
> > > > From: Peng Fan <peng.fan@xxxxxxx>
> > > >
> > > > 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@xxxxxxx>
> > > > ---
> > > >  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.

It is just my ATF not initialize the shmem area the leave the area with random
data.

So I think that some released buggy firmware might also has similar issue.

To support buggy firmware and bug-fixed firmware, I think it might be helpful
to init shmem in Linux side.

Thanks,
Peng.

> 
> > 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