Re: [PATCH 2/2] firmware: arm_scmi: Add compatibility checks for shmem node

From: Florian Fainelli <f.fainelli@gmail.com>
To: Sudeep Holla <sudeep.holla@arm.com>,
	Etienne Carriere <etienne.carriere@linaro.org>
Cc: "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE"
	<linux-arm-kernel@lists.infradead.org>,
	Cristian Marussi <cristian.marussi@arm.com>,
	Kevin Hilman <khilman@baylibre.com>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Jim Quinlan <jim2101024@gmail.com>
Subject: Re: [PATCH 2/2] firmware: arm_scmi: Add compatibility checks for shmem node
Date: Thu, 3 Jun 2021 10:18:20 -0700	[thread overview]
Message-ID: <0963a5e1-5ce2-4ef4-7ff9-cbbea0f974d0@gmail.com> (raw)
In-Reply-To: <20210602075326.clypj7qmiv4gebas@bogus>

On 6/2/21 12:53 AM, Sudeep Holla wrote:
> On Wed, Jun 02, 2021 at 09:44:40AM +0200, Etienne Carriere wrote:
>> On Wed, 2 Jun 2021 at 09:37, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>>
>>> On Wed, Jun 02, 2021 at 09:33:03AM +0200, Etienne Carriere wrote:
>>>> Hello Sudeep,
>>>>
>>>>
>>>> On Wed, 2 Jun 2021 at 00:51, Sudeep Holla <sudeep.holla@arm.com> wrote:
>>>>>
>>>>> The shared memory node used for communication between the firmware and
>>>>> the OS should be compatible with "arm,scmi-shmem". Add the check for the
>>>>> same while parsing the node before fetching the memory regions.
>>>>>
>>>>> Cc: Cristian Marussi <cristian.marussi@arm.com>
>>>>> Cc: Florian Fainelli <f.fainelli@gmail.com>
>>>>> Cc: Jim Quinlan <jim2101024@gmail.com>
>>>>> Cc: Etienne Carriere <etienne.carriere@linaro.org>
>>>>> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
>>>>> ---
>>>>>  drivers/firmware/arm_scmi/mailbox.c | 3 +++
>>>>>  drivers/firmware/arm_scmi/smc.c     | 3 +++
>>>>>  2 files changed, 6 insertions(+)
>>>>>
>>>>> diff --git a/drivers/firmware/arm_scmi/mailbox.c b/drivers/firmware/arm_scmi/mailbox.c
>>>>> index 4626404be541..e3dcb58314ae 100644
>>>>> --- a/drivers/firmware/arm_scmi/mailbox.c
>>>>> +++ b/drivers/firmware/arm_scmi/mailbox.c
>>>>> @@ -69,6 +69,9 @@ static int mailbox_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>>>>>                 return -ENOMEM;
>>>>>
>>>>>         shmem = of_parse_phandle(cdev->of_node, "shmem", idx);
>>>>> +       if (!of_device_is_compatible(shmem, "arm,scmi-shmem"))
>>>>> +               return -ENXIO;
>>>>
>>>> Before this change, one could use another type of memory node, like "mmio-sram".
>>>> Is there a strong reason to enforce use of "arm,scmi-shmem" nodes?
>>>>
>>>
>>> No that is for the entire SRAM which still holds and generic on-chip SRAM
>>> driver will take care of that, this is only for the subsections that is
>>> reserved for the scp shmem. The binding has been always there, just the
>>> missing check. When I move to yaml, I realised that and hence the
>>> addition of check.
>>
>> Ok, I understand. True the binding was there but only in the DTS
>> examples snipped.
>> This constraint on the compatible property of the shmem node should be
>> clearly stated in the yaml I think.
>>
> 
> Was this missing in your DTS files ? Just curious.
> 

FWIW, our legacy DTs would have the following:

	reserved-memory {
                /* This is a placeholder */
                NWMBOX: NWMBOX {
                };
        };

       brcm_scmi: brcm_scmi@0 {
                compatible = "arm,scmi-smc", "arm,scmi";
                mboxes = <&brcm_scmi_mailbox 0>, <&brcm_scmi_mailbox 1>;
                mbox-names = "tx", "rx";
                shmem = <&NWMBOX>;
                status = "disabled";

so while we have since switched to the SMC transport, the shared memory
still does not have an "arm,scmi-shmem" compatible string, and this is a
relatively new thing, so I am not sure we can enforce that just yet?
-- 
Florian

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