> On Jun 27, 2017, at 11:11 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Jun 27, 2017 at 06:32:07PM -0600, Philip Prindeville wrote: >> I’m running 3.10.0 (CentOS 7.3) on a Supermicro X10SDV-8C-TLN4F >> motherboard, which has a 16550A on it. > > That's really old and obsolete, and not supported by the community at > all. Care to use a more modern kernel? :) I’m happy to fix it on HEAD or linux-next and then back-port the fix. But for this particular server, I’m required to run CentOS 7.3 on it. > >> What’s odd is that when I look in /dev/ I see ttyS0…S3, even though >> there are only 2 hardware ports (a single DUART). >> >> [root@kvm2 logwatch]# setserial -G /dev/ttyS0 >> /dev/ttyS0 uart 16550A port 0x03f8 irq 4 baud_base 115200 spd_normal skip_test >> [root@kvm2 logwatch]# setserial -G /dev/ttyS1 >> /dev/ttyS1 uart 16550A port 0x02f8 irq 3 baud_base 115200 spd_normal skip_test >> [root@kvm2 logwatch]# setserial -G /dev/ttyS2 >> /dev/ttyS2 uart unknown port 0x03e8 irq 4 baud_base 115200 spd_normal skip_test >> [root@kvm2 logwatch]# setserial -G /dev/ttyS3 >> /dev/ttyS3 uart unknown port 0x02e8 irq 3 baud_base 115200 spd_normal >> >> >> and dmesg says: >> >> [ 3.173481] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled >> [ 3.194077] 00:03: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A >> [ 3.214710] 00:04: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A >> >> >> I was trying to figure out where this happens, and why, so maybe I >> could submit a patch to allow one to suppress this behavior (say with >> “8250.only_real_hw=1” or some other module parameter). >> >> Not sure where this is happening. Thought it might be in >> drivers/tty/serial/8250/8250_pnp.c but nothing stands out. >> >> Anyone know the backstory on why this happens, and how to >> (conditionally) change this behavior? > > Why do you need to change this? What is wrong with the existing way > this works? As for the code that implements it, it's the platform > driver for your system that thinks the serial ports are there to remain > compatible with the old PC standard. Why do I want to change it? Well, why would I want to keep it? If I open /dev/ttyS2 or /dev/ttyS3 they're not useful for anything at all, since they don’t correspond to existing hardware. Why have them? I already have /dev/null if I need something that I can’t read from and that writing to amounts to throwing away data... -Philip > > thanks, > > greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
