From mboxrd@z Thu Jan 1 00:00:00 1970 From: okaya@codeaurora.org (okaya at codeaurora.org) Date: Tue, 29 Mar 2016 08:15:42 -0400 Subject: [PATCH V3 1/3] vfio, platform: add support for ACPI while detecting the reset driver In-Reply-To: <147496989.L43SVC7xRY@wuerfel> References: <1459172124-6730-1-git-send-email-okaya@codeaurora.org> <98854818.NJS35fvhsb@wuerfel> <147496989.L43SVC7xRY@wuerfel> Message-ID: <8f766d081b33d91f196e7bd5e13b6f33@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 2016-03-29 07:25, Arnd Bergmann wrote: > On Tuesday 29 March 2016 06:59:15 okaya at codeaurora.org wrote: >> On 2016-03-29 05:25, Arnd Bergmann wrote: >> > On Monday 28 March 2016 09:35:22 Sinan Kaya wrote: >> >> The code is using the compatible DT string to associate a reset driver >> >> with >> >> the actual device itself. The compatible string does not exist on ACPI >> >> based systems. HID is the unique identifier for a device driver >> >> instead. >> >> The change allows a driver to register with DT compatible string or >> >> ACPI >> >> HID and then match the object with one of these conditions. >> >> >> >> Rules for loading the reset driver are as follow: >> >> - ACPI HID needs match for ACPI systems >> >> - DT compat needs to match for OF systems >> >> >> >> Tested-by: Eric Auger (device tree only) >> >> Tested-by: Shanker Donthineni (ACPI only) >> >> Signed-off-by: Sinan Kaya >> >> >> > >> > >> > This really feels wrong for two reasons: >> > >> > * device assignment of non-PCI devices is really special and doesn't >> > seem to make sense on general purpose servers that would be the >> > target >> > for ACPI normally >> >> >> Why is it special? Acpi is not equal to pci. Platform devices are >> first >> class devices too. Especially, _cls was introduced for this reason. > > It still feels like a hack. The normal design for a server is to have > all internal devices show up on the PCI host bridge, next to the PCIe > ports, to have a simple way to manage any device, both internal and > off-chip. Putting a device on random MMIO registers outside of the > discoverable buses and have the firmware work around the lack of > discoverability will always be inferior. > It is a HW implementation choice. Having everything as pci problem has been already solved. I would vote for it when we had SW pci bridge layer just to use usb and sata. Not anymore. Especially, _cls solves this problem >> > >> > * If there is indeed a requirement for ACPI to handle something like >> > this, >> > it should be part of the ACPI spec, with a well-defined method of >> > handling >> > reset, rather than having to add a device specific hack for each >> > device separately. >> > >> >> I see. Normally, this is done by calling _rst method. AFAIK, Linux >> doesn?t support _rst. I can check its presence and call it if it is >> there. > > Yes, that sounds reasonable: In patch 2 where you check for the > presence of the reset method, just keep the existing logic for > DT based systems, and use _rst on ACPI based systems instead, > then you can drop both patches 1 and 3. > I can certainly drop patch #3 and push the reset responsibility to acpi. I never liked having a fragmented sw design across multiple drivers. I need something for patch #1. Compatible is a DT property not ACPI.but then, I won't have a reset driver anymore. If we think about how vfio pci works, we pass the pci vendor and device id to new_id file to find out which pci device needs to be pass thru. I can go to a similar route. This time we pass the object id through new_id and I call reset method on this object. Let me know what you think? > Arnd