Return-Path: Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.0 \(3445.1.7\)) Subject: Re: [PATCH 2/2] ACPI / scan: Fix enumeration for special UART devices From: Marcel Holtmann In-Reply-To: <20171009090835.GQ2618@localhost> Date: Mon, 9 Oct 2017 20:09:19 +0200 Cc: Sebastian Reichel , =?utf-8?Q?Fr=C3=A9d=C3=A9ric_Danis?= , robh@kernel.org, loic.poulain@gmail.com, lukas@wunner.de, hdegoede@redhat.com, linux-bluetooth@vger.kernel.org, linux-serial@vger.kernel.org, linux-acpi@vger.kernel.org Message-Id: References: <1507107090-15992-1-git-send-email-frederic.danis.oss@gmail.com> <1507107090-15992-3-git-send-email-frederic.danis.oss@gmail.com> <20171007151934.GJ2618@localhost> <20171007225311.lvli7rkhv3bebq2j@earth> <20171009073526.GL2618@localhost> <20171009085534.c5smytfgckyx7mqy@earth> <20171009090835.GQ2618@localhost> To: Johan Hovold Sender: linux-serial-owner@vger.kernel.org List-ID: Hi Johan, >>>>>> UART devices is expected to be enumerated by SerDev subsystem. >>>>>> >>>>>> During ACPI scan, serial devices behind SPI, I2C or UART buses are not >>>>>> enumerated, allowing them to be enumerated by their respective parents. >>>>>> >>>>>> Rename *spi_i2c_slave* to *serial_bus_slave* as this will be used for serial >>>>>> devices on serial buses (SPI, I2C or UART). >>>>>> >>>>>> On Macs an empty ResourceTemplate is returned for uart slaves. >>>>>> Instead the device properties "baud", "parity", "dataBits", "stopBits" are >>>>>> provided. Add a check for "baud" in acpi_is_serial_bus_slave(). >>>>>> >>>>>> Signed-off-by: Frédéric Danis >>>>> >>>>> So just to reiterate what I just mentioned in a comment to one of Hans's >>>>> hci_bcm patches: >>>>> >>>>> This one would silently break PM for such devices on any system which >>>>> does not have serdev enabled (as the corresponding platform devices >>>>> would no longer be registered). And with serdev enabled, hciattach >>>>> (btattach) would start failing as the tty device would no longer be >>>>> registered (but I assume everyone is aware of that, and fine with it, by >>>>> now). >>>>> >>>>> Perhaps the hci_bcm driver should start depending on >>>>> SERIAL_DEV_CTRL_TTYPORT when ACPI is enabled? >>>> >>>> ACPI and DT both need SERIAL_DEV_CTRL_TTYPORT to work properly, >>>> since SERIAL_DEV_CTRL_TTYPORT is the only controller implemented >>>> for serdev. If any other controller is implemented that one could >>>> also be used. >>> >>> Not for hci_bcm, right? This particular driver specifically depends on >>> SERIAL_DEV_CTRL_TTYPORT for the ACPI devices and not just any (future) >>> serdev controller (or currently working systems soon breaks silently). >>> >>> I don't think the same is true for the DT case where we do not already >>> have child nodes defined in firmware (and in fact, this driver did not >>> really support DT before serdev). >> >> The serdev ACPI support has been added to the core and not to >> the ttyport and the hci_bcm driver only uses functions from the >> core. As far as I can see the ACPI part would also work fine with >> a different serdev controller. > > Indeed, but you need SERIAL_DEV_CTRL_TTYPORT to avoid silently breaking > current ACPI setups which breaks when this patch is applied (as these > devices all hang off of common serial ports managed by serial core). > >> Of course DT and ACPI currently require SERIAL_DEV_CTRL_TTYPORT, >> since it's the only serdev controller implementation. Also it >> covers most use cases. When SERIAL_DEV_BUS is selected it's >> very likely, that you also want SERIAL_DEV_CTRL_TTYPORT. > >>>> I wonder if we should just hide SERIAL_DEV_CTRL_TTYPORT and enable >>>> it together with SERDEV. I suspect that we won't see any other >>>> controller (it would be a UART device, that is not registered as >>>> tty device) in the next few years and the extra option seems to >>>> confuse people. >>> >>> I agree that it is somewhat confusing. But now that we have both, >>> perhaps simply having SERIAL_DEV_CTRL_TTYPORT default to "y" when >>> SERIAL_DEV_BUS is selected could be a compromise. The Kconfig entry >>> might need to be amended as well (e.g. if only to mention that you >>> need to select a controller as well). >> >> I think we should at least add a default "y" if SERIAL_DEV_BUS. > > I'm preparing a patch. yes, please prepare a patch since the discussion spans multiple email threads now. Lets get this back on track and find a patch that we are all happy with. Regards Marcel