On Fri, Dec 4, 2020 at 3:41 AM Greg KH gregkh@linuxfoundation.org wrote:
On Wed, Dec 02, 2020 at 04:54:24PM -0800, Dan Williams wrote:
From: Dave Ertman david.m.ertman@intel.com
Add support for the Auxiliary Bus, auxiliary_device and auxiliary_driver. It enables drivers to create an auxiliary_device and bind an auxiliary_driver to it.
The bus supports probe/remove shutdown and suspend/resume callbacks. Each auxiliary_device has a unique string based id; driver binds to an auxiliary_device based on this id through the bus.
Co-developed-by: Kiran Patil kiran.patil@intel.com Co-developed-by: Ranjani Sridharan ranjani.sridharan@linux.intel.com Co-developed-by: Fred Oh fred.oh@linux.intel.com Co-developed-by: Leon Romanovsky leonro@nvidia.com Signed-off-by: Kiran Patil kiran.patil@intel.com Signed-off-by: Ranjani Sridharan ranjani.sridharan@linux.intel.com Signed-off-by: Fred Oh fred.oh@linux.intel.com Signed-off-by: Leon Romanovsky leonro@nvidia.com Signed-off-by: Dave Ertman david.m.ertman@intel.com Reviewed-by: Pierre-Louis Bossart pierre-louis.bossart@linux.intel.com Reviewed-by: Shiraz Saleem shiraz.saleem@intel.com Reviewed-by: Parav Pandit parav@mellanox.com Reviewed-by: Dan Williams dan.j.williams@intel.com Reviewed-by: Martin Habets mhabets@solarflare.com Link: https://lore.kernel.org/r/20201113161859.1775473-2-david.m.ertman@intel.com Signed-off-by: Dan Williams dan.j.williams@intel.com
This patch is "To:" the maintainers that have a pending backlog of driver updates dependent on this facility, and "Cc:" Greg. Greg, I understand you have asked for more time to fully review this and apply it to driver-core.git, likely for v5.12, but please consider Acking it for v5.11 instead. It looks good to me and several other stakeholders. Namely, stakeholders that have pressure building up behind this facility in particular Mellanox RDMA, but also SOF, Intel Ethernet, and later on Compute Express Link.
I will take the blame for the 2 months of silence that made this awkward to take through driver-core.git, but at the same time I do not want to see that communication mistake inconvenience other parties that reasonably thought this was shaping up to land in v5.11.
I am willing to host this version at:
git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux tags/auxiliary-bus-for-5.11
...for all the independent drivers to have a common commit baseline. It is not there yet pending Greg's Ack.
For example implementations incorporating this patch, see Dave Ertman's SOF series:
https://lore.kernel.org/r/20201113161859.1775473-2-david.m.ertman@intel.com
...and Leon's mlx5 series:
http://lore.kernel.org/r/20201026111849.1035786-1-leon@kernel.org
PS: Greg I know I promised some review on newcomer patches to help with your queue, unfortunately Intel-internal review is keeping my plate full. Again, I do not want other stakeholder to be waiting on me to resolve that backlog.
Ok, I spent some hours today playing around with this. I wrote up a small test-patch for this (how did anyone test this thing???) and while it feels awkward in places, and it feels like there is still way too much "boilerplate" code that a user has to write and manage, I don't have the time myself to fix it up right now.
So I'll go apply this to my tree, and provide a tag for everyone else to be able to pull from for their different development trees so they can work on.
I do have 3 follow-on patches that I will send to the list in response to this message that I will be applying on top of this patch. They do some minor code formatting changes, as well as change the return type of the remove function to make it more future-proof. That last change will require users of this code to change their implementations, but it will be obvious what to do as you will get a build warning.
Note, I'm still not comfortable with a few things here. The documentation feels odd, and didn't really help me out in writing any test code, which doesn't seem right. Also the use of strings and '.' as part of the api feels awkward, and messy, and of course, totally undocumented.
But, as the use of '.' is undocumented, that means we can change it in the future! Because no driver or device name should ever be a user api reliant thing, if we come up with a better way to do all of this in the future, that shouldn't be a problem to change existing users over to this. So this is a warning to everyone, you CAN NOT depend on the sysfs name of a device or bus name for any tool. If so, your userspace tool is broken.
Thanks for everyone in sticking with this, I know it's been a long slog, hopefully this will help some driver authors move forward with their crazy complex devices :)
To me, the documentation was written, and reviewed, more from the perspective of "why not open code a custom bus instead". So I can see after the fact how that is a bit too much theory and justification and not enough practical application. Before the fact though this was a bold mechanism to propose and it was not clear that everyone was grokking the "why" and the tradeoffs.
I also think it was a bit early to identify consistent design patterns across the implementations and codify those. I expect this to evolve convenience macros just like other parts of the driver-core gained over time. Now that it is in though, another pass through the documentation to pull in more examples seems warranted.