Re: [PATCH v3 12/16] PCI/DOE: Create mailboxes on device enumeration

[Alexey Kardashevskiy <aik@amd.com>]

On 28/2/23 16:43, Lukas Wunner wrote:
> On Tue, Feb 28, 2023 at 12:18:07PM +1100, Alexey Kardashevskiy wrote:
>> On 11/2/23 07:25, Lukas Wunner wrote:
>>> For the same reason a DOE instance cannot be shared between the PCI core
>>> and a driver.
>>
>> And we want this sharing why? Any example will do. Thanks,
> 
> The PCI core is going to perform CMA/SPDM authentication when a device
> gets enumerated (PCIe r6.0 sec 6.31).  That's the main motivation
> to lift DOE mailbox creation into the PCI core.  It's not mentioned
> here explicitly because I want the patch to stand on its own.
> CMA/SPDM support will be submitted separately.

I was going the opposite direction with avoiding adding this into the 
PCI core as 1) the pci_dev struct is already 2K  and 2) it is a niche 
feature and  3) I wanted this CMA/SPDM session setup to be platform 
specific as on our platform the SPDM support requires some devices to be 
probed before we can any SPDM.


> A driver that later on gets bound to the device should be allowed
> to talk to it via DOE as well, possibly even sharing the same DOE
> mailboxes used by the PCI core.
> 
> Patches for CMA/SPDM are under development on this branch:
> 
> https://github.com/l1k/linux/commits/doe

yes, thanks! Lots of reading :)


>>> Currently a DOE instance cannot be shared by multiple drivers because
>>> each driver creates its own pci_doe_mb struct for a given DOE instance.
>>
>> Sorry for my ignorance but why/how/when would a device have multiple drivers
>> bound? Or it only one driver at the time but we also want DOE MBs to survive
>> switching to another (different or newer) driver?
> 
> Conceivably, a driver may have the need to talk to multiple devices
> via DOE, even ones it's not bound to.  (E.g. devices in its ancestry
> or children.)

Ah ok. Well, a parent device could look for the DOE MB in a child using 
devres_find(), this requirement alone does not require moving things to 
the PCI core and potentially allows it to be a module which could be a 
better way as distros could have it always enabled but it would not 
waste any memory on my laptop when not loaded. Thanks,


-- 
Alexey