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Message-ID: <696170b9-1cd7-ecce-a318-aa5013855275@quicinc.com>
Date: Mon, 17 Apr 2023 11:17:06 -0700
From: Nikunj Kela <quic_nkela@...cinc.com>
To: Florian Fainelli <f.fainelli@...il.com>, <sudeep.holla@....com>
CC: <cristian.marussi@....com>, <robh+dt@...nel.org>,
<krzysztof.kozlowski+dt@...aro.org>,
<linux-arm-kernel@...ts.infradead.org>,
<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/2] firmware: arm_scmi: Augment SMC/HVC to allow
optional parameter
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@...cinc.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) {
>
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