[PATCH v3 2/2] firmware: arm_scmi: Augment SMC/HVC to allow optional parameter

[Nikunj Kela]

On 4/17/2023 11:01 AM, Florian Fainelli wrote:
> On 4/17/23 10:44, Nikunj Kela wrote:
>> This patch add support for passing shmem channel address as parameter
>> in smc/hvc call. This patch is useful when multiple scmi instances are
>> using same smc-id and firmware needs to distiguish among the instances.
>
> Typo: distinguish.
>
Will fix it.
> It really would have been a lot clearer and made a whole lot more 
> sense to encode a VM ID/channel number within some of the SMCCC 
> parameters, possibly as part of the function ID itself.
smc-id(func-id) is 32 bit long and the spec doesn't define any such 
provisions in it. Having said that, there are optional parameters as 
session-id and client-id(secureOS-id) that can be passed in w6/r6 and 
w7/r7 registers. If maintainers are OK to use dtb to pass them instead, 
I can rework the patches.
>
>>
>> Signed-off-by: Nikunj Kela <quic_nkela at quicinc.com>
>> ---
>>   drivers/firmware/arm_scmi/driver.c |  1 +
>>   drivers/firmware/arm_scmi/smc.c    | 25 ++++++++++++++++++++++++-
>>   2 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/firmware/arm_scmi/driver.c 
>> b/drivers/firmware/arm_scmi/driver.c
>> index e7d97b59963b..b5957cc12fee 100644
>> --- a/drivers/firmware/arm_scmi/driver.c
>> +++ b/drivers/firmware/arm_scmi/driver.c
>> @@ -2914,6 +2914,7 @@ static const struct of_device_id 
>> scmi_of_match[] = {
>>   #endif
>>   #ifdef CONFIG_ARM_SCMI_TRANSPORT_SMC
>>       { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
>> +    { .compatible = "arm,scmi-smc-param", .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 93272e4bbd12..e28387346d33 100644
>> --- a/drivers/firmware/arm_scmi/smc.c
>> +++ b/drivers/firmware/arm_scmi/smc.c
>> @@ -20,6 +20,9 @@
>>     #include "common.h"
>>   +#define lower32(x)    ((u32)((x) & 0xffffffff))
>> +#define upper32(x)    ((u32)(((u64)(x) >> 32) & 0xffffffff))
>
> Cannot you use the existing lower_32_bits and upper_32_bits macros 
> from kernel.h here?
>
>> +
>>   /**
>>    * struct scmi_smc - Structure representing a SCMI smc transport
>>    *
>> @@ -30,6 +33,8 @@
>>    * @inflight: Atomic flag to protect access to Tx/Rx shared memory 
>> area.
>>    *          Used when operating in atomic mode.
>>    * @func_id: smc/hvc call function id
>> + * @is_smc64: smc/hvc calling convention type 64 vs 32
>> + * @param: physical address of the shmem channel
>>    */
>>     struct scmi_smc {
>> @@ -40,6 +45,8 @@ struct scmi_smc {
>>   #define INFLIGHT_NONE    MSG_TOKEN_MAX
>>       atomic_t inflight;
>>       u32 func_id;
>> +    bool is_smc64;
>> +    phys_addr_t param;
>>   };
>>     static irqreturn_t smc_msg_done_isr(int irq, void *data)
>> @@ -137,6 +144,8 @@ static int smc_chan_setup(struct scmi_chan_info 
>> *cinfo, struct device *dev,
>>       if (ret < 0)
>>           return ret;
>>   +    if (of_device_is_compatible(dev->of_node, "arm,scmi-smc-param"))
>> +        scmi_info->param = res.start;
>
> There is not even a check that this is going to be part of the 
> kernel's view of memory, that seems a bit brittle and possibly a 
> security hole, too. Your hypervisor presumably needs to have carved 
> out some amount of memory in order for the messages to be written 
> to/read from, and so would the VM kernel, so eventually we should have 
> a 'reserved-memory' entry of some sort, no?
>
>>       /*
>>        * If there is an interrupt named "a2p", then the service and
>>        * completion of a message is signaled by an interrupt rather 
>> than by
>> @@ -156,6 +165,7 @@ static int smc_chan_setup(struct scmi_chan_info 
>> *cinfo, struct device *dev,
>>       }
>>         scmi_info->func_id = func_id;
>> +    scmi_info->is_smc64 = ARM_SMCCC_IS_64(func_id);
>>       scmi_info->cinfo = cinfo;
>>       smc_channel_lock_init(scmi_info);
>>       cinfo->transport_info = scmi_info;
>> @@ -188,7 +198,20 @@ 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, 0, 0, 0, 0, 0, 0, 0, 
>> &res);
>> +#ifdef CONFIG_ARM64
>> +    /*
>> +     * if SMC32 convention is used, pass 64 bit address in
>> +     * two parameters
>> +     */
>> +    if (!scmi_info->is_smc64)
>
> There is no need for scmi_info to store is_smc64, just check the 
> func_id here and declare is_smc64 as a local variable to the function.
>
> Also, another way to approach this would be to encode the parameters 
> region in 4KB units such that event on a 32-bit system with LPAE you 
> are guaranteed to fit the region into a 32-bit unsigned long. AFAIR 
> virtualization and LPAE are indistinguishable on real CPUs?
>
>> + arm_smccc_1_1_invoke(scmi_info->func_id,
>> +                     lower32(scmi_info->param),
>> +                     upper32(scmi_info->param),
>> +                     0, 0, 0, 0, 0, &res);
>> +    else
>> +#endif
>> +        arm_smccc_1_1_invoke(scmi_info->func_id, scmi_info->param,
>> +                     0, 0, 0, 0, 0, 0, &res);
>>         /* Only SMCCC_RET_NOT_SUPPORTED is valid error code */
>>       if (res.a0) {
>