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Wysocki" , Lukas Wunner , linux-kernel@vger.kernel.org References: <20180424082954.11453-1-shrirang.bagul@canonical.com> <20180424171846.GD4615@localhost> From: Hans de Goede Message-ID: Date: Tue, 24 Apr 2018 23:16:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180424171846.GD4615@localhost> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-serial-owner@vger.kernel.org X-Mailing-List: linux-serial@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Hi, On 24-04-18 19:18, Johan Hovold wrote: > [ Adding some more people on CC. ] > > On Tue, Apr 24, 2018 at 04:29:53PM +0800, Shrirang Bagul wrote: >> On systems using Intel Atom (Baytrail-I) SoC's, slave devices connected on >> HSUART1/2 ports are described by the ACPI BIOS as virtual hardware using >> HID's INT3511/INT3512 [1]. >> >> As a consequence, HW manufacturers have complete freedom to install any >> devices on-board as long as they can be accessed over serial tty >> interface. Once such device is Dell Edge 3002 IoT Gateway which sports >> ZigBee & GPS devices on the HS-UART ports 1 & 2 respectively. >> >> In kernels before the introduction of 'Serial Device Bus (serdev)' >> subsystem, these devices were accessible using /dev/ttySx nodes. But, >> kernels since 4.15 can no longer do so. >> >> Post 4.15, with CONFIG_SERIAL_DEV_BUS=y, serdev port controller driver >> handles the enumeration for the slaves connected on these ports. Also, >> /dev/ttySx device nodes for these ports are no longer exposed to the >> userspace. >> >> This patch implements a new driver which binds to the ACPI serdev slaves >> enumerated by the serdev port controller and exposes /dev/ttyHSx device >> nodes which the userspace applications can use. Otherwise, upgrades to 4.15 >> or higher kernels would certainly render these devices unusable. >> >> Considering serdev is new and evolving, this is one approach to solving >> the problem at hand. An obvious drawback is the change in the tty device >> node name from ttySx => ttyHSx, which means userspace applications have to >> be modified (I know that this is strongly discouraged). For the same >> reason, I am submitting these patches as RFC. >> >> If there are other/better ways of solving this or improving on the >> proposed solution, that will be most helpful. > > Yeah, I don't think this is the right solution to this problem. It seems > we need to blacklist (or maybe even use whitelists) ACPI-ids until there > are drivers for the slave devices that would otherwise be claimed by > serdev. FWIW I've been using this patch for a while for realtek UART attached bluetooth: https://github.com/jwrdegoede/linux-sunxi/commit/bc904e3703940600ca66c65fcdb0a8cb01dff55d which is a gross hack. If we're going to do a whitelist for this, it better support some sort of wildcards as there are a LOT of BCM2E?? devices which need to be on the whitelist. I think a blacklist would actually be better though, this also documents which devices are lacking a proper kernel (where applicable). Regards, Hans > >> This patch is based on: >> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v4.17-rc2 >> >> [1] Enabling Multi-COM Port for Microsoft Windows OS 8.1 & 10 / IoT Core [Sec. 4.1] >> (https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/enabling-multi-com-port-white-paper.pdf) > > Thanks, > Johan >