Hi Werner, Ron, Nico, list,
While it would be great to not have to implement Bus Master
workarounds in coreboot, I guess it's sometimes unavoidable because of
external constraints. I would much prefer to have the actual problem
fixed instead (code assuming Bus Master is enabled by default), but if
that's not possible I can live with some mechanism to enable Bus
Master in coreboot, *as long as all usages are justified*. IMHO,
enabling Bus Master for no reason is bad practice, but keeping code to
enable Bus Master because no one knows what removing it could break is
On Tue, Nov 10, 2020 at 3:24 PM werner.zeh(a)siemens.com
We could introduce a Kconfig switch per driver
Not per-driver, please!
I'd rather have per-reason switches (reason-options): Kconfig options
whose help-text gives the reason why enabling Bus Master in coreboot
for certain devices is needed. Even if these Kconfig options end up
being scattered across the tree, it's easier to see the relationship
between multiple instances of Bus Master being set. Plus, if the
actual bug is eventually fixed, it's very easy to drop the
corresponding reason-option without breaking any other reason-options.
and let the driver handle the bit.
Everything else could be removed. This would make it easier to track the usages.
It would be nice if we could agree on a naming scheme so that all switches are named
similar which would make it easier to track the usage.
But there are cases where there is no driver in coreboot for a given PCI device which
needs this bit. For now, we (Siemens) handle this cases on mainboard level.
So either we need drivers for these devices (just simply setting the master bit) or we
can agree on some kind of exceptions.
I am open to everything.
This won't be a problem if using per-reason Kconfig options. I would
still use these reason-options though, even when the option always
gets selected (e.g. selected by the mainboard's Kconfig): this is to
justify each instance of Bus Master being set with the corresponding
Von: ron minnich <rminnich(a)gmail.com>
Gesendet: Dienstag, 10. November 2020 16:15
An: Nico Huber <nico.h(a)gmx.de>
Cc: coreboot <coreboot(a)coreboot.org>
Betreff: [coreboot] Re: Deprecating spurious PCI bus master enabling (was Re: Planning
the next coreboot release)
On Tue, Nov 10, 2020 at 7:13 AM Nico Huber <nico.h(a)gmx.de> wrote:
On 10.11.20 16:06, Nico Huber wrote:
If anybody knows or discovers more cases where it
needs to be
enabled in advance by coreboot, please mention it here.
We just discussed on IRC cases where unfixable OS drivers might need it.
For such cases, it would probably be best to add individual Kconfig
switches for each case. This would make it easier to get rid of the
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