On Tue, Nov 11, 2014 at 9:35 AM, Rob Herring <robh@xxxxxxxxxx> wrote: >> What is the current best practice for new drivers? > > I think it would be using dynamic numbering, but would be good to have > others weigh in here. It looks like a dynamic major would solve your > problem. See tty_register_driver. Also, there was a patch to make this > the fallback behavior instead of an error[1], but it was never merged > (and it's not clear why). This was the Samsung related change I was > remembering. > > Rob > > [1] http://lists.linaro.org/pipermail/linaro-kernel/2014-January/010383.html This doesn't seem to fix the coexistence problems with the 8250 driver. Perhaps it is time to write a simpler version of the 8250 driver geared toward embedded applications? Some items on my wishlist include: - OF_EARLYCON support - Native-endian and big-endian register support - Move to a pure runtime-enumerated model and drop the ISA code - Drop support for obsolete chips (16450, 8250) and quirks for obsolete PCs It looks like sunsu, serial-tegra, omap-serial, and possibly others have already started down this path. Or I could just write a dedicated uart_bcm7xxx driver if that's easier... Here are my results after grabbing V2 of Tushar's patch from the list archives and reverting the bcm63xx_uart driver to claim "ttyS" with major 4, minor 64: - Building with CONFIG_SERIAL_8250_NR_UARTS=0 rendered the 8250-based system unbootable (it dies with no output right after the bootconsole is disabled) - Building with CONFIG_SERIAL_8250_NR_UARTS=1 rendered the bcm63xx_uart-based system unbootable, with the following output: Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled Default device node (4:64) for ttyS is busy, using dynamic major number bcm63xx_uart 10000100.serial: ttyS0 at MMIO 0x10000100 (irq = 28, base_baud = 1562500) is a bcm63xx_uart console [ttyS0] enabled console [ttyS0] enabled bootconsole [uart0] disabled bootconsole [uart0] disabled ------------[ cut here ]------------ WARNING: CPU: 0 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x64/0xbc() sysfs: cannot create duplicate filename '/class/tty/ttyS0' CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.18.0-rc4+ #384 Stack : 00000000 00000004 00000000 80075444 00000000 00000000 00000000 00000000 809e5012 0000003a 00000001 00000000 00010000 87c282b8 8056dac4 805b9ce7 00000001 00000000 809e39d8 87c282b8 87c6ae10 00000001 87c6ae10 804edeb0 805c0000 80032984 00000000 00000000 80571d28 87c2da84 87c2da84 8056dac4 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 ... Call Trace: [<8001a00c>] show_stack+0x64/0x7c [<804eff94>] dump_stack+0xc8/0xfc [<80032bd8>] warn_slowpath_common+0x7c/0xac [<80032c68>] warn_slowpath_fmt+0x2c/0x38 [<8015c784>] sysfs_warn_dup+0x64/0xbc [<8015cabc>] sysfs_do_create_link_sd.isra.2+0xec/0xf4 [<802c193c>] device_add+0x4b0/0x59c [<802a452c>] tty_register_device_attr+0xe4/0x278 [<802b625c>] uart_add_one_port+0x344/0x474 [<802bbffc>] bcm_uart_probe+0x14c/0x240 [<802c6c20>] platform_drv_probe+0x54/0xc4 [<802c51bc>] really_probe+0xa0/0x2cc [<802c5544>] __driver_attach+0xd0/0xd8 [<802c3660>] bus_for_each_dev+0x68/0xb0 [<802c4160>] bus_add_driver+0x168/0x230 [<802c5f6c>] driver_register+0x84/0x138 [<805e86ec>] bcm_uart_init+0x30/0x58 [<805d4ce0>] do_one_initcall+0x148/0x208 [<805d4f0c>] kernel_init_freeable+0x16c/0x228 [<804eb6dc>] kernel_init+0x10/0x100 [<80013ce8>] ret_from_kernel_thread+0x14/0x1c ---[ end trace dc92a8c272541296 ]--- bcm63xx_uart 10000100.serial: Cannot register tty device on line 0 libphy: Fixed MDIO Bus: probed usbcore: registered new interface driver asix usbcore: registered new interface driver ax88179_178a usbcore: registered new interface driver cdc_ether usbcore: registered new interface driver net1080 usbcore: registered new interface driver cdc_subset usbcore: registered new interface driver zaurus usbcore: registered new interface driver cdc_ncm ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver ehci-platform: EHCI generic platform driver ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver ohci-platform: OHCI generic platform driver usbcore: registered new interface driver usb-storage TCP: cubic registered NET: Registered protocol family 10 sit: IPv6 over IPv4 tunneling driver NET: Registered protocol family 17 Freeing unused kernel memory: 4144K (805d4000 - 809e0000) starting pid 797, tty '': '/etc/init.d/rcS' Mounting virtual filesystems Starting mdev Configuring lo interface Configuring sit0 interface Starting network services starting pid 826, tty '': '/bin/cttyhack /bin/sh -l' process '/bin/cttyhack /bin/sh -l' (pid 826) exited. Scheduling for restart. starting pid 828, tty '': '/bin/cttyhack /bin/sh -l' process '/bin/cttyhack /bin/sh -l' (pid 828) exited. Scheduling for restart. starting pid 830, tty '': '/bin/cttyhack /bin/sh -l'
