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[71.163.245.5]) by smtp.gmail.com with ESMTPSA id v65sm6511846qkb.88.2020.10.26.05.37.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Oct 2020 05:37:47 -0700 (PDT) Subject: Re: [PATCH 10/11] [DEBUG] firmware: arm_scmi: add custom_dummy SCMI devname To: Cristian Marussi Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, sudeep.holla@arm.com, lukasz.luba@arm.com, james.quinlan@broadcom.com, Jonathan.Cameron@Huawei.com, f.fainelli@gmail.com, etienne.carriere@linaro.org, vincent.guittot@linaro.org, souvik.chakravarty@arm.com References: <20201014150545.44807-1-cristian.marussi@arm.com> <20201014150545.44807-11-cristian.marussi@arm.com> <20201021113505.GD20482@e120937-lin> From: Thara Gopinath Message-ID: <7658875c-ea5f-d231-9514-5021e9d62807@linaro.org> Date: Mon, 26 Oct 2020 08:37:46 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201021113505.GD20482@e120937-lin> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/21/20 7:35 AM, Cristian Marussi wrote: > On Tue, Oct 20, 2020 at 10:49:23PM -0400, Thara Gopinath wrote: >> >> >> On 10/14/20 11:05 AM, Cristian Marussi wrote: >>> Add custom_dummy SCMI devname. >>> >>> Signed-off-by: Cristian Marussi >>> --- >>> drivers/firmware/arm_scmi/driver.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c >>> index 55df134c2338..5c39a738866a 100644 >>> --- a/drivers/firmware/arm_scmi/driver.c >>> +++ b/drivers/firmware/arm_scmi/driver.c >>> @@ -993,6 +993,7 @@ static struct scmi_prot_devnames devnames[] = { >>> { SCMI_PROTOCOL_CLOCK, { "clocks" },}, >>> { SCMI_PROTOCOL_SENSOR, { "hwmon" },}, >>> { SCMI_PROTOCOL_RESET, { "reset" },}, >>> + { SCMI_PROTOCOL_CUSTOM_DUMMY, { "custom_dummy" },}, >> >> Hi Cristian, >> >> Thanks for the sample dummy custom protocol and driver! >> The problem with adding scmi devname into the array is that every time a >> custom vendor protocol is added, the array has to be extended. Instead since >> the scmi spec supports the range 0x80-0xff for custom protocols, why not >> check for that range in scmi_create_protocol_devices and go ahead with >> registering the creating the protocol device via >> scmi_create_protocol_device? >> > > Hi, > > so this is really a good point, and in fact in some earlier (non-public) > iterations I had a mechanism to just get rid of these device tables, > thinking that if you want to enable custom protocols loading, it seemed > better to let the related devices being created dynamically at will, so > that an SCMI driver can just 'declare' its own device name and that will > be created if the corresponding protocol is found in the DT and > implemented in fw. > > Anyway this complicated the code a lot in some dubious ways. > > In a built-in scenario you end up with your driver being probe before the > platform SCMI driver, so you cannot create the device straight away in > your driver (there's not even an SCMI bus still) and you anyway need the > platform SCMI driver to be up and running to check the DT and initialize > basic transport to talk to the fw and check the protocol is supported by > fw before creating the device itself: so I ended up basically having the > SCMI driver just 'requesting' some device name to the core and then having > the core creating the device later on when the SCMI platform was probed > iff the DT and the fw supported that protocol (or immediately if your > driver was a module and the SCMI platform was already initialized) > > All of the above, even if working, led to a lot of machinery to track all > these requested devices properly and properly create/destroy them, and > also it does not seem the right thing to do, since it's basically > mimicing/duplicating all the usual probe deferring standard mechanism. > > Maybe this could have been addressed in different ways but I've not > explored further. > > So at the end I removed such dynamic device creation support from this > series. > > Now you proposal would be, if I understood correctly, to just create > straight away a custom device whenever its protocol is defined in the DT > and supported by fw, so that the custom driver above would not have to > declare anything statically, and it will just be associated with some > "dev_proto_99" matching just on protocol number. > > I'd like this option because it simplifies a lot the above issues, but > I don't think it is viable because in this way you are no more able to > define 2 distinct SCMI drivers for the same protocol (like you > can do now defining multiple names in the match table: as an example you > could not create a different "custom_dummy_2" SCMI driver using the > custom protocol 0x99, because there;s only one single "dev_proto_99" > device created and already probed for "custom_dummy". Hi, Apologies for the delay in this reply as it took me a while to figure out in the code what is happening around this. So if I understand you correctly, the table is required to support multiple drivers (which is today 2) for a protocol which in turn means creating devices for these drivers. But drivers/firmware/arm_scmi/driver.c is the wrong place to define these dev names. Like any other device/driver pair in the kernel , why is this info not conveyed from DT ? It should be fairly straightforward to have scmi_dev_match_id to match the device compatible string passed via dt node with a driver that is attached to scmi_bus. Now, the questions is, is there any existing implementation that requires 2 separate devices with 2 separate drivers for a protocol? I am using 2 here because MAX_SCMI_DEV_PER_PROTOCOL is defined as 2 today in the framework. If not, I will just drop this and just create a device for every protocol that gets conveyed from DT. If yes, I will look at passing that info from DT either as a compatible string or as a number so that you can dynamically build the name when creating device. The problem with this table is every time anyone wants to support a new driver, the table has to be updated. Ideally, framework files should not require any modification to support an extension protocol. > > So the problem is again that if you want to support multiple SCMI > drivers they have to be able to declare their own devname, against which > the platform SCMI driver can match and initialized if needed the > underlying device. > > In short, I want certainly to explore the dynamic device creation > further, but for the moment I put it apart trying to consolidate > all the rest. > > Maybe I could re-introduce something better later on in future versions > of this series, or maybe just address this a distinct series later on. > > Sorry for the flood-style email :D No issues! > > Thanks > > Cristian > >> >>> }; >>> static inline void >>> >> >> -- >> Warm Regards >> Thara -- Warm Regards Thara