Re: [PATCH] serial: Skip over PCIe device which have no quirks (fix AMT regression).

[Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>]

On 3/5/2014 3:09 PM, Konrad Rzeszutek Wilk wrote:
> See:
> 00:16.0 Communication controller: Intel Corporation Cougar Point HECI Controller #1 (rev 04)
>          Subsystem: Intel Corporation Device 2008
>          Flags: bus master, fast devsel, latency 0, IRQ 11
>          Memory at fb12a000 (64-bit, non-prefetchable) [size=16]
> 00:16.3 Serial controller: Intel Corporation Cougar Point KT Controller (rev 04) (prog-if 02 [16550])
>          Subsystem: Intel Corporation Device 2008
>          Flags: bus master, 66MHz, fast devsel, latency 0, IRQ 17
>          I/O ports at f0e0 [size=8]
>          Memory at fb129000 (32-bit, non-prefetchable) [size=4K]
>
> pci 0000:00:16.0: [8086:1c3a] type 00 class 0x078000
> pci 0000:00:16.3: [8086:1c3d] type 00 class 0x070002
>
> And Xen picks 00:16.0 as its console when using 'com1=115200,8n1,amt'.
>
> This patch fixes it and allows us to use AMT again by zeroing
> out io_base to zero. If the scan did not work, the io_base is
> set back to a default value.

If you provide 'amt' on command line => 'skip_amt' = 0
Then we'd just return -1 without setting io_base to 0x3f8 due to this 
condition-
if ( !skip_amt )
    return -1;

(or am I missing something?)

>
> diff --git a/xen/drivers/char/ns16550.c b/xen/drivers/char/ns16550.c
> index 487bf7d..9f87018 100644
> --- a/xen/drivers/char/ns16550.c
> +++ b/xen/drivers/char/ns16550.c
> @@ -829,6 +829,7 @@ pci_uart_config (struct ns16550 *uart, int skip_amt, int bar_idx)
>       unsigned int b, d, f, nextf, i;
>       u16 vendor, device;
>   
> +    uart->io_base = 0;

Why not set ns16550.io_base = 0; in arch/x86/setup.c ?
AFAICT, ns16550.c is the only one that uses ns16550_defaults structure, 
so it should be safe..


Thanks,
-Aravind.