Hi Rafael,
On 14/03/18 11:57, Rafael J. Wysocki wrote:
On Wednesday, March 14, 2018 12:50:54 PM CET Tomasz Figa wrote:
On Wed, Mar 14, 2018 at 8:12 PM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote:
On Tuesday, March 13, 2018 12:23:34 PM CET Tomasz Figa wrote:
On Tue, Mar 13, 2018 at 7:34 PM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
Hi Tomasz,
On Tue, Mar 13, 2018 at 3:45 PM, Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
Hi Vivek,
Thanks for the patch.
On Tue, Mar 13, 2018 at 5:55 PM, Vivek Gautam
<vivek.gautam@xxxxxxxxxxxxxx> wrote:
The lists managing the device-links can be traversed to
find the link between two devices. The device_link_add() APIs
does traverse these lists to check if there's already a link
setup between the two devices.
So, add a new APIs, device_link_find(), to find an existing
device link between two devices - suppliers and consumers.
I'm wondering if this API would be useful for anything else that the
problem we're trying to solve with deleting links without storing them
anywhere. Perhaps a device_link_del_dev(consumer, supplier) would be a
better alternative?
Yea, that sounds simpler i think. Will add this API instead of
find_link(). Thanks.
Perhaps let's wait for a moment to see if there are other opinions. :)
Rafael, Lucas, any thoughts?
It is not clear to me what the device_link_del_dev(consumer, supplier) would do.
It would delete a link between consumer and supplier.
If there's one I suppose.
I'm wondering if you are somehow trying to address the same problem as the
device links reference counting patch from Lukas that has been queued up for 4.17
already.
Not quite - the issue here is that we have one supplier with an
arbitrarily large number of consumers, and would prefer that supplier
not to have to spend a whole bunch of memory to store all the struct
device_link pointers for the sole reason of having something to give to
device_link_del() at the end, given that the device links code is
already keeping track of everything internally anyway.
The current API would permit doing this:
iommu_attach(dev) {
...
if (!device_link_add(dev, iommu, IOMMU_LINK_FLAGS))
return -ENODEV;
...
}
iommu_detach(dev) {
...
// Will return the existing link from earlier
link = device_link_add(dev, iommu, IOMMU_LINK_FLAGS);
device_link_del(link);
// Needed once refcounting is in place
//device_link_del(link);
...
}
but it looks so wacky and non-obvious that we'd like to encapsulate the
same behaviour into a more formal interface (my personal naming
preference would be device_link_remove(consumer, supplier)).
Robin.
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