Re: [PATCH v4 4/4] firmware: arm_scmi: Add qcom hvc/shmem transport support

[Sudeep Holla]

On Tue, Oct 03, 2023 at 09:16:27AM -0700, Nikunj Kela wrote:
> 
> On 10/3/2023 4:19 AM, Sudeep Holla wrote:
> > On Mon, Sep 11, 2023 at 12:43:59PM -0700, Nikunj Kela wrote:
> > > This change adds the support for SCMI message exchange on Qualcomm
> > > virtual platforms.
> > > 
> > > The hypervisor associates an object-id also known as capability-id
> > > with each hvc doorbell object. The capability-id is used to identify the
> > > doorbell from the VM's capability namespace, similar to a file-descriptor.
> > > 
> > > The hypervisor, in addition to the function-id, expects the capability-id
> > > to be passed in x1 register when HVC call is invoked.
> > > 
> > > The function-id & capability-id are allocated by the hypervisor on bootup
> > > and are stored in the shmem region by the firmware before starting Linux.
> > > 
> > > Signed-off-by: Nikunj Kela <quic_nkela@xxxxxxxxxxx>
> > > ---
> > >   drivers/firmware/arm_scmi/driver.c |  1 +
> > >   drivers/firmware/arm_scmi/smc.c    | 47 ++++++++++++++++++++++++++----
> > >   2 files changed, 43 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> > > index 87383c05424b..ea344bc6ae49 100644
> > > --- a/drivers/firmware/arm_scmi/driver.c
> > > +++ b/drivers/firmware/arm_scmi/driver.c
> > > @@ -2915,6 +2915,7 @@ static const struct of_device_id scmi_of_match[] = {
> > >   #ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
> > >   	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> > >   	{ .compatible = "arm,scmi-smc-param", .data = &scmi_smc_desc},
> > > +	{ .compatible = "qcom,scmi-hvc-shmem", .data = &scmi_smc_desc},
> > >   #endif
> > >   #ifdef CONFIG_ARM_SCMI_TRANSPORT_VIRTIO
> > >   	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
> > > diff --git a/drivers/firmware/arm_scmi/smc.c b/drivers/firmware/arm_scmi/smc.c
> > > index 0a0b7e401159..94ec07fdc14a 100644
> > > --- a/drivers/firmware/arm_scmi/smc.c
> > > +++ b/drivers/firmware/arm_scmi/smc.c
> > > @@ -50,6 +50,9 @@
> > >    * @func_id: smc/hvc call function id
> > >    * @param_page: 4K page number of the shmem channel
> > >    * @param_offset: Offset within the 4K page of the shmem channel
> > > + * @cap_id: hvc doorbell's capability id to be used on Qualcomm virtual
> > > + *	    platforms
> > > + * @qcom_xport: Flag to indicate the transport on Qualcomm virtual platforms
> > >    */
> > >   struct scmi_smc {
> > > @@ -63,6 +66,8 @@ struct scmi_smc {
> > >   	u32 func_id;
> > >   	u32 param_page;
> > >   	u32 param_offset;
> > > +	u64 cap_id;
> > Can it be unsigned long instead so that it just works for both 32 and 64 bit.
> 
> My first version of this patch was ulong but Bjorn suggested to make this
> structure size fixed i.e. architecture independent. Hence changed it to u64.
> If you are ok with ulong, I can change it back to ulong.
>

SMCCC pre-v1.2 used the common structure in that way. I don't see any issue
with that. I haven't followed Bjorn suggestions/comments though.

> 
> > 
> > > +	bool qcom_xport;
> > Do we really need this ?
> 
> Not if we initialize it with a negative value since 0 is a valid value for
> cap-id.
>

Fine with negative value(-EINVAL may be).

> > >   	int ret;
> > >   	if (!tx)
> > > @@ -158,9 +164,34 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> > >   		return -EADDRNOTAVAIL;
> > >   	}
> > > -	ret = of_property_read_u32(dev->of_node, "arm,smc-id", &func_id);
> > > -	if (ret < 0)
> > > -		return ret;
> > > +	if (of_device_is_compatible(dev->of_node, "qcom,scmi-hvc-shmem")) {
> > > +		scmi_info->qcom_xport = true;
> > > +
> > > +		/* The func-id & capability-id are kept in last 16 bytes of shmem.
> > > +		 *     +-------+
> > > +		 *     |       |
> > > +		 *     | shmem |
> > > +		 *     |       |
> > > +		 *     |       |
> > > +		 *     +-------+ <-- (size - 16)
> > > +		 *     | funcId|
> > > +		 *     +-------+ <-- (size - 8)
> > > +		 *     | capId |
> > > +		 *     +-------+ <-- size
> > > +		 */
> > > +
> > > +		func_id = readl((void __iomem *)(scmi_info->shmem) + size - 16);
> > So unlike 'arm,scmi-smc', you don't want 'arm,smc-id' in the DT ? Any
> > particular reason ? Just to get both FID and cap ID from shmem ?
>

I am fine either way. If you use from DT(via arm,smc-id), then "qcom,scmi"
can be just addition compatible that expects you to read cap-id from the
shmem. May need adjustment in the binding as you allow both
"qcom,scmi-smc", "arm,scmi-smc". I will leave the details to you.

> I could use smc-id binding for func-id, it's just two parameters will come
> from two different places so thought of keeping everything at one place to
> maintain consistency.  Since DT can't take cap-id, I decided to move
> func-id. I am fine if you want me to use smc-id binding.
>

Up to you. If you want to make "qcom,scmi-smc" and "arm,scmi-smc"
compatible in way in that way or you can keep it incompatible as you have
proposed in this patch set.

> 
> > > +#ifdef CONFIG_ARM64
> > I would rather make this arch agnostic using CONFIG_64BIT
> ok.
> > 
> > > +		cap_id = readq((void __iomem *)(scmi_info->shmem) + size - 8);
> > Do you need __iomem typecast here ? Is scmi_info->shmem not already __iomem ?
> > Also scmi_info->shmem is ioremapped just few steps above and you are using
> > read* here, is that safe ?
> 
> I saw some compilation warnings without __iomem. I will use ioread* API
> instead of read*.
>

That was the clue that you were using __iomem with read* calls IMO.

> 
> > 
> > > +#else
> > > +		/* capability-id is 32 bit wide on 32bit machines */
> > > +		cap_id = rieadl((void __iomem *)(scmi_info->shmem) + size - 8);
> > Other thought once you move for u64 to unsigned long you need not have
> > #ifdeffery, just do copy of sizeof(unsigned long)
> Right, my first version was like that only.

OK

> > 
> > > +#endif
> > > +	} else {
> > > +		ret = of_property_read_u32(dev->of_node, "arm,smc-id", &func_id);
> > > +		if (ret < 0)
> > > +			return ret;
> > > +	}
> > >   	if (of_device_is_compatible(dev->of_node, "arm,scmi-smc-param")) {
> > >   		scmi_info->param_page = SHMEM_PAGE(res.start);
> > > @@ -184,6 +215,7 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> > >   	}
> > >   	scmi_info->func_id = func_id;
> > > +	scmi_info->cap_id = cap_id;
> > >   	scmi_info->cinfo = cinfo;
> > >   	smc_channel_lock_init(scmi_info);
> > >   	cinfo->transport_info = scmi_info;
> > > @@ -213,6 +245,7 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
> > >   	struct arm_smccc_res res;
> > >   	unsigned long page = scmi_info->param_page;
> > >   	unsigned long offset = scmi_info->param_offset;
> > > +	unsigned long cap_id = (unsigned long)scmi_info->cap_id;
> > >   	/*
> > >   	 * Channel will be released only once response has been
> > > @@ -222,8 +255,12 @@ static int smc_send_message(struct scmi_chan_info *cinfo,
> > >   	shmem_tx_prepare(scmi_info->shmem, xfer, cinfo);
> > > -	arm_smccc_1_1_invoke(scmi_info->func_id, page, offset, 0, 0, 0, 0, 0,
> > > -			     &res);
> > > +	if (scmi_info->qcom_xport)
> > Just make sure cap_id is set only for qcom and just use that as your flag.
> > No point in setting always true scmi_info->qcom_xport and using it here.
> ok, I can remove that. Though 0 is a valid value for cap-id so will have to
> init cap-id with a negative value.

Yes as mentioned above.

-- 
Regards,
Sudeep