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[2001:1c00:c0c:fe00:d2ea:f29d:118b:24dc]) by smtp.gmail.com with ESMTPSA id ng1sm6972407ejb.112.2020.12.06.02.43.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 06 Dec 2020 02:43:14 -0800 (PST) Subject: Re: [PATCH v2 0/9] Add support for Microsoft Surface System Aggregator Module To: Maximilian Luz , Leon Romanovsky , =?UTF-8?Q?Bla=c5=be_Hrastnik?= Cc: Greg Kroah-Hartman , lkml , Mark Gross , Andy Shevchenko , =?UTF-8?Q?Barnab=c3=a1s_P=c5=91cze?= , Arnd Bergmann , Rob Herring , Jiri Slaby , "Rafael J . Wysocki" , Len Brown , Steven Rostedt , Ingo Molnar , Masahiro Yamada , Michal Marek , Jonathan Corbet , Dorian Stoll , platform-driver-x86@vger.kernel.org, linux-serial@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org References: <20201203212640.663931-1-luzmaximilian@gmail.com> <20201206070705.GA686270@unreal> <052ecf4d-9e08-2c08-8a06-c30ba2b28d82@redhat.com> <1b4fe1fd-592d-4a88-b156-fbf6af2df428@www.fastmail.com> <20201206090614.GA693271@unreal> From: Hans de Goede Message-ID: <8c6f7234-fc7e-66c2-948c-1232eb5ff813@redhat.com> Date: Sun, 6 Dec 2020 11:43:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi, On 12/6/20 11:33 AM, Maximilian Luz wrote: > On 12/6/20 10:06 AM, Leon Romanovsky wrote:> On Sun, Dec 06, 2020 at 05:58:32PM +0900, Blaž Hrastnik wrote: >>>> >>>>> More on that, the whole purpose of proposed interface is to debug and >>>>> not intended to be used by any user space code. >>>> >>>> The purpose is to provide raw access to the Surface Serial Hub protocol, >>>> just like we provide raw access to USB devices and have hidraw devices. >>>> >>>> So this goes a litle beyond just debugging; and eventually the choice >>>> may be made to implement some functionality with userspace drivers, >>>> just like we do for some HID and USB devices. >>>> >>>> Still I agree with you that adding new userspace API is something which >>>> needs to be considered carefully. So I will look at this closely when >>>> reviewing this set. >>> >>> To add to that: this was previously a debugfs interface but was moved to misc after review on the initial RFC: >>> https://lkml.org/lkml/2020/9/24/96 >> >> There is a huge difference between the suggestion and final implementation. >> >> Greg suggested to add new debug module to the drivers/misc that will >> open char device explicitly after user loaded that module to debug this >> hub. However, the author added full blown char device as a first citizen >> that has all not-break-user constrains. > > This module still needs to be loaded explicitly. Good then I really do not see a problem with this. > And (I might be wrong > about this) the "not-break-user constraints" hold as soon as I register > a misc device at all, no? Correct. > So I don't see how this is a) any different > than previously discussed with Greg and b) how the uapi header now > introduces any not-break-user constraints that would not be there > without it. > > This interface is intended as a stable interface. That's something that > I committed to as soon as I decided to implement this via a misc-device. > > Sure, I can move the definitions in the uapi header to the module > itself, but I don't see any benefit in that. Right, if we are going to use a misc chardev for this, then the correct thing to do is to put the API bits for that chardev under include/uapi. It would still be good if you can provide a pointer to some userspace tools using this new API; and for the next version maybe add that pointer to the commit message Regards, Hans