Re: [PATCH v2 2/8] firmware: arm_scmi: introduce protocol handles

[Etienne Carriere]

Hello Thara,

On Wed, 4 Nov 2020 at 17:16, Thara Gopinath <thara.gopinath@xxxxxxxxxx> wrote:
>
>
> Hi Cristian,
>
> On 10/28/20 4:29 PM, Cristian Marussi wrote:
> > Add basic protocol handles definitions and helpers support.
> > All protocols initialization code and SCMI drivers probing is still
> > performed using the handle based interface.
> >
> > Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>
> > ---
> >   drivers/firmware/arm_scmi/common.h | 61 ++++++++++++++++++++++++++++
> >   drivers/firmware/arm_scmi/driver.c | 64 ++++++++++++++++++++++++++++++
> >   2 files changed, 125 insertions(+)
> >
> > diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> > index b08a8ddbc22a..f0678be02a09 100644
> > --- a/drivers/firmware/arm_scmi/common.h
> > +++ b/drivers/firmware/arm_scmi/common.h
> > @@ -151,6 +151,67 @@ int scmi_xfer_get_init(const struct scmi_handle *h, u8 msg_id, u8 prot_id,
> >                      size_t tx_size, size_t rx_size, struct scmi_xfer **p);
> >   void scmi_reset_rx_to_maxsz(const struct scmi_handle *handle,
> >                           struct scmi_xfer *xfer);
> > +
> > +struct scmi_xfer_ops;
> > +
> > +/**
> > + * struct scmi_protocol_handle  - Reference to an initialized protocol instance
> > + *
> > + * @dev: A reference to the associated SCMI instance device (handle->dev).
> > + * @xops: A reference to a struct holding refs to the core xfer operations that
> > + *     can be used by the protocol implementation to generate SCMI messages.
> > + * @set_priv: A method to set protocol private data for this instance.
> > + * @get_priv: A method to get protocol private data previously set.
> > + *
> > + * This structure represents a protocol initialized against specific SCMI
> > + * instance and it will be used as follows:
> > + * - as a parameter fed from the core to the protocol initialization code so
> > + *   that it can access the core xfer operations to build and generate SCMI
> > + *   messages exclusively for the specific underlying protocol instance.
> > + * - as an opaque handle fed by an SCMI driver user when it tries to access
> > + *   this protocol through its own protocol operations.
> > + *   In this case this handle will be returned as an opaque object together
> > + *   with the related protocol operations when the SCMI driver tries to access
> > + *   the protocol.
> > + */
> > +struct scmi_protocol_handle {
> > +     struct device *dev;
> > +     const struct scmi_xfer_ops *xops;
> > +     int (*set_priv)(const struct scmi_protocol_handle *ph, void *priv);
> > +     void *(*get_priv)(const struct scmi_protocol_handle *ph);
> > +};
>
> So scmi_xfer_ops are the ops that actually talks with the scmi firmware
> on the other end , right ? IIUC, these ops are the same for all the
> protocols of a scmi instance. Imho, this struct is not the right place
> for these ops to reside.You are inadvertently exposing scmi internal
> details to the client drivers. There is no reason why this should be
> part of scmi_handle. The protocols can extract it from the handle during
> protocol_reigster, right?
>
> So, now to the second part, why do you need a scmi_protocol_handle?
> Again IIUC, if you have set_priv and get_priv hooks and get_ops and
> put_ops hooks, there is nothing that scmi_protocol_handle is providing
> extra, right? As mentioned in the comments for last patch any reason all
> of this cannot be rolled into scmi_protocol?
>
> As long as you are not supporting multiple scmi_protocol_instance and
> scmi_protocol_handle for a protocol, I don't think having separate
> structs make sense.

This is a scenario SCMI can face. Consider system with several
contained firmwares
(multi-coprocs) each can expose SCMI services hence multi protocol instances.
I.e 2 coproc each exposing some of their clocks to Linux that registers them.

Regards,
Etienne

> And you need to do this only if you think there can
> be multiple versions/instances of a protocol in the same scmi instance.
> Or am I missing something here ?
>
> > +
> > +/**
> > + * struct scmi_xfer_ops  - References to the core SCMI xfer operations.
> > + * @version_get: Get this version protocol.
> > + * @xfer_get_init: Initialize one struct xfer if any xfer slot is free.
> > + * @reset_rx_to_maxsz: Reset rx size to max transport size.
> > + * @do_xfer: Do the SCMI transfer.
> > + * @do_xfer_with_response: Do the SCMI transfer waiting for a response.
> > + * @xfer_put: Free the xfer slot.
> > + *
> > + * Note that all this operations expect a protocol handle as first parameter;
> > + * they then internally use it to infer the underlying protocol number: this
> > + * way is not possible for a protocol implementation to forge messages for
> > + * another protocol.
> > + */
> > +struct scmi_xfer_ops {
> > +     int (*version_get)(const struct scmi_protocol_handle *ph, u32 *version);
> > +     int (*xfer_get_init)(const struct scmi_protocol_handle *ph, u8 msg_id,
> > +                          size_t tx_size, size_t rx_size,
> > +                          struct scmi_xfer **p);
> > +     void (*reset_rx_to_maxsz)(const struct scmi_protocol_handle *ph,
> > +                               struct scmi_xfer *xfer);
> > +     int (*do_xfer)(const struct scmi_protocol_handle *ph,
> > +                    struct scmi_xfer *xfer);
> > +     int (*do_xfer_with_response)(const struct scmi_protocol_handle *ph,
> > +                                  struct scmi_xfer *xfer);
> > +     void (*xfer_put)(const struct scmi_protocol_handle *ph,
> > +                      struct scmi_xfer *xfer);
> > +};
> > +
> > +struct scmi_revision_info *
> > +scmi_get_revision_area(const struct scmi_protocol_handle *ph);
> >   int scmi_handle_put(const struct scmi_handle *handle);
> >   struct scmi_handle *scmi_handle_get(struct device *dev);
> >   void scmi_set_handle(struct scmi_device *scmi_dev);
> > diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> > index beae8991422d..8ca04acb6abb 100644
> > --- a/drivers/firmware/arm_scmi/driver.c
> > +++ b/drivers/firmware/arm_scmi/driver.c
> > @@ -72,19 +72,28 @@ struct scmi_xfers_info {
> >
> >   /**
> >    * struct scmi_protocol_instance  - Describe an initialized protocol instance.
> > + * @handle: Reference to the SCMI handle associated to this protocol instance.
> >    * @proto: A reference to the protocol descriptor.
> >    * @gid: A reference for per-protocol devres management.
> >    * @users: A refcount to track effective users of this protocol.
> > + * @priv: Reference for optional protocol private data.
> > + * @ph: An embedded protocol handle that will be passed down to protocol
> > + *   initialization code to identify this instance.
> >    *
> >    * Each protocol is initialized independently once for each SCMI platform in
> >    * which is defined by DT and implemented by the SCMI server fw.
> >    */
> >   struct scmi_protocol_instance {
> > +     const struct scmi_handle        *handle;
> >       const struct scmi_protocol      *proto;
> >       void                            *gid;
> >       refcount_t                      users;
> > +     void                            *priv;
> > +     struct scmi_protocol_handle     ph;
> >   };
> >
> > +#define ph_to_pi(h)  container_of(h, struct scmi_protocol_instance, ph)
> > +
> >   /**
> >    * struct scmi_info - Structure representing a SCMI instance
> >    *
> > @@ -543,6 +552,57 @@ int scmi_version_get(const struct scmi_handle *handle, u8 protocol,
> >       return ret;
> >   }
> >
> > +/**
> > + * scmi_set_protocol_priv  - Set protocol specific data at init time
> > + *
> > + * @ph: A reference to the protocol handle.
> > + * @priv: The private data to set.
> > + *
> > + * Return: 0 on Success
> > + */
> > +static int scmi_set_protocol_priv(const struct scmi_protocol_handle *ph,
> > +                               void *priv)
> > +{
> > +     struct scmi_protocol_instance *pi = ph_to_pi(ph);
> > +
> > +     pi->priv = priv;
> > +
> > +     return 0;
> > +}
> > +
> > +/**
> > + * scmi_get_protocol_priv  - Set protocol specific data at init time
> > + *
> > + * @ph: A reference to the protocol handle.
> > + *
> > + * Return: Protocol private data if any was set.
> > + */
> > +static void *scmi_get_protocol_priv(const struct scmi_protocol_handle *ph)
> > +{
> > +     const struct scmi_protocol_instance *pi = ph_to_pi(ph);
> > +
> > +     return pi->priv;
> > +}
> > +
> > +/**
> > + * scmi_get_revision_area  - Retrieve version memory area.
> > + *
> > + * @ph: A reference to the protocol handle.
> > + *
> > + * A helper to grab the version memory area reference during SCMI Base protocol
> > + * initialization.
> > + *
> > + * Return: A reference to the version memory area associated to the SCMI
> > + *      instance underlying this protocol handle.
> > + */
> > +struct scmi_revision_info *
> > +scmi_get_revision_area(const struct scmi_protocol_handle *ph)
> > +{
> > +     const struct scmi_protocol_instance *pi = ph_to_pi(ph);
> > +
> > +     return pi->handle->version;
> > +}
> > +
> >   /**
> >    * scmi_get_protocol_instance  - Protocol initialization helper.
> >    * @handle: A reference to the SCMI platform instance.
> > @@ -588,6 +648,10 @@ scmi_get_protocol_instance(struct scmi_handle *handle, u8 protocol_id)
> >
> >               pi->gid = gid;
> >               pi->proto = proto;
> > +             pi->handle = handle;
> > +             pi->ph.dev = handle->dev;
> > +             pi->ph.set_priv = scmi_set_protocol_priv;
> > +             pi->ph.get_priv = scmi_get_protocol_priv;
> >               refcount_set(&pi->users, 1);
> >               /* proto->init is assured NON NULL by scmi_protocol_register */
> >               ret = pi->proto->init(handle);
> >
>
> --
> Warm Regards
> Thara