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SubjectRe: [PATCH] firewire: reread config ROM when device reset the bus
Kristian Høgsberg wrote:
> On Mon, Mar 3, 2008 at 11:51 AM, Stefan Richter
> <> wrote:
> ...
>> Maybe I should rather use fw-device.c::idr_rwsem instead of device.sem,
>> to have better control over who takes the mutex when. Could also be a
>> new dedicated mutex but we don't want to end up with too many of them...
>> Do you have an opinion?
> Using the struct device mutex is fine, and it parallelizes better than
> the global idr_mutex (FWIW). The only concern I have there is that
> the device core structs seem to change now and then, and it's not
> clear what is implementation details and what is exported for drivers
> to use (eg the subsystem sem).

This may be more of a concern to anybody who wanted to change the driver
core internals and might be unsure what to do with those three dev->sem
taking sites which I added; not so much a concern from the firewire
driver maintenance POV.

OTOH, contention for idr_rwsem is low and there can be multiple readers
of course. The most time consuming thing that could happen would be
waiting for GFP_KERNEL allocations of new IDR tree leaves. And maybe
having the dev->sem in a cacheline but idr_rwsem not is probably not a
concern for the stuff that the writer and the two readers of the ROM
cache do.

Ah, wait, there is a 3rd reader: sbp2_probe's sbp2_scan_unit_dir. So,
using dev->sem is actually the nicest way for now.
Stefan Richter
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