Message-ID: <d22b0da7-fc52-549f-20ad-3829379dccff@quicinc.com>
Date:   Wed, 4 Oct 2023 10:48:58 -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 10/4/2023 9:06 AM, Sudeep Holla wrote:
> 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@...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.
>>
> 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.
Ok.
>>>> +	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).
Ok.
>>>>    	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.
Ok.
>> 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.
Ok.
>>>> +#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.
Ok.
>>>> +#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.
Ok.
>

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