On Thursday, January 22, 2015 11:57:55 AM Alexandre Courbot wrote: > On Wed, Jan 21, 2015 at 6:25 AM, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > On Tuesday, January 20, 2015 01:16:06 PM Linus Walleij wrote: > >> On Mon, Jan 19, 2015 at 6:59 AM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote: > >> > >> > I am not really fond of this idea since it adds complexity to the > >> > (already too complex) GPIO lookup, and only solves to a local level > >> > (GPIO) what is a more global problem (bad ACPI tables that can affect > >> > any subsystem). > >> (...) > >> > it > >> > seems more to-the-point to find a way to fix/patch the ACPI tables at > >> > runtime, if that is possible at all, to provide a more general > >> > solution to this issue. > >> > >> This is my position as well, until proven that this cannot be done. > > > > Well, that goes against the current practice, mind you, which *is* to put > > workarounds for buggy ACPI tables into the kernel. I'm not going to defend > > that, but it has been done for several years now. > > > > Also someone may say to that: "Why don't *you* demonstrate that it can be done > > in the first place?" And what if it can be done, but is too complex to be > > practical or similar? > > > > My personal opinion is that having a way to apply a fix on top of broken ACPI > > tables (or an extension on top of correct ones for that matter) without touching > > the kernel would be very useful indeed, but making it secure may be somewhat > > challenging, because in principle there's no reason why the kernel should trust > > such "external" fixes. > > > >> In device tree the same mechanism is called "device tree overlays" > >> and I just have some vague feeling that such stuff is patched around in > >> some Intel platforms already, but maybe that involves replacing > >> the whole DSDT from userspace, > > > > From initramfs rather than from user space, but yes, it does. > > > >> surely the mechanism can be refined? > > > > Yes, it can (in principle). In fact, we have a plan to refine it, but it is > > going to take some time. Once we've done that, we'll see how painful it is to > > "patch" ACPI tables this way in practice. > > > > Also there is an ecosystem problem related to distributing such "patches". > > Today, distributions don't need to worry about patching buggy platform > > firmware, because they get workarounds in the kernel, but if we switch over > > to the model in which platform firmware "overlays" need to be provided in > > addition to it, then suddenly questions arise about who should be responsible > > for making them available, how to avoid duplication of efforts between > > distributions etc. > > > > All of that needs to be clarified before we start making hard statements like > > "No in-kernel workarounds for that!" > > > > And, of course, there's the question of what the kernel should do if the given > > firmware patch is not effective, so it doesn't really fix the problem it is > > supposed to fix or it fixes that problem only partially or, worse yet, it > > introuces more bugs than it fixes. Should the kernel simply fail then (and > > in what way if so) or should it try to carry out some default "sanitization" > > of what the firmare (and patch) tells it and try to continue on the best > > effort basis? > > If we decide to go ahead with the solution proposed by this patch for > practical reasons (which are good reasons indeed), I still have one > problem with its current form. > > As the discussion highlighted, this is an ACPI problem, so I'd very > much like it to be confined to the ACPI GPIO code, to be enabled only > when ACPI is, and to use function names that start with acpi_gpio. I can agree with that. > The current implementation leverages platform lookup, making said lookup > less efficient in the process and bringing confusion about its > purpose. Although the two processes are indeed similar, they are > separate things: one is a legitimate way to map GPIOs, the other is a > fixup for broken firmware. > > I suppose we all agree this is a hackish fix, so let's confine it as > much as we can. OK Heikki, any comments? -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
