Message-ID: <6246714a-3b40-e1b6-640e-560ba55b6436@quicinc.com>
Date:   Tue, 3 Oct 2023 09:16:27 -0700
From:   Nikunj Kela <quic_nkela@...cinc.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     <cristian.marussi@....com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 4/4] firmware: arm_scmi: Add qcom hvc/shmem transport
 support


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@...cinc.com>
>> ---
>>   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.


>
>> +	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.


>
>>   };
>>   
>>   static irqreturn_t smc_msg_done_isr(int irq, void *data)
>> @@ -129,6 +134,7 @@ static int smc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>>   	struct resource res;
>>   	struct device_node *np;
>>   	u32 func_id;
>> +	u64 cap_id;
> Ditto..

Answered in earlier comment.


>>   	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 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.


>> +#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*.


>
>> +#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.
>
>> +#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.
>
>> +		arm_smccc_1_1_hvc(scmi_info->func_id, cap_id, 0, 0, 0, 0, 0, 0,
>> +				  &res);
>> +	else
>> +		arm_smccc_1_1_invoke(scmi_info->func_id, page, offset, 0, 0, 0,
>> +				     0, 0, &res);
>>   
>>   	/* Only SMCCC_RET_NOT_SUPPORTED is valid error code */
>>   	if (res.a0) {
>> -- 
>> 2.17.1
>>

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