Re: [PATCH 4/5] thunderbolt: Correlate PCI devices with Thunderbolt ports

[Mika Westerberg]

Hi Lukas,

On Sun, Sep 09, 2018 at 11:42:01PM +0200, Lukas Wunner wrote:
> Ideas what we can do with correlation:
> 
> * Represent the relationship between PCI devices and Thunderbolt ports
>   with symlinks in sysfs.

I wonder is that really useful? I don't think we should be adding sysfs
entries without any real reason why it would be needed and who would be
using them.

> * Thunderbolt controllers up to revision 1 of Cactus Ridge 4C have to
>   use INTx because MSI signaling is broken.  This results in hotplug
>   ports sharing interrupts with other devices and, when daisy-chaining
>   multiple affected Thunderbolt controllers, can lead to extremely
>   unbalanced interrupt usage.  To avoid this we could prefer downstream
>   ports for tunnel establishment which do not share interrupts (based
>   on the nr_actions field of the correlated PCI device's irq_desc).
> 
> * Alternatively, we could use non-working MSI signaling on affected
>   controllers and synthesize an interrupt whenever a tunnel is
>   established or goes down on unplug.

Problem I see with this patch as it stands is that you add 200+ lines of
code into the driver that is not being used by anything as far as I
understand it.