Hi, On 2/28/22 19:19, Rafael J. Wysocki wrote: > +Mika, Andy and Hans in case they have something to add Thanks, I don't really have anything to add to the discussion on v6 of this patch. Regards, Hans > > On Mon, Feb 28, 2022 at 12:27 AM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: >> >> Hey again, >> >> On Sun, Feb 27, 2022 at 1:43 PM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: >>> >>> Hi Alex, >>> >>> On Sun, Feb 27, 2022 at 12:42:03PM +0100, Alexander Graf wrote: >>>>> To allow device drivers to match identifiers that exceed the 9 byte >>>>> limit, this simply ups the length to 16, just like it was before the >>>>> aforementioned commit. Empirical testing indicates that this >>>> >>>> >>>> This is only true for 64bit systems where padding automatically bloated >>>> to 9 byte array to 16. I still believe the patch is fine as it is, but >>>> there will be minor .rodata overhead on 32bit targets which you may want >>>> to quantify in the patch description. >>> >>> Good point. So I just tried this out with a 32-bit i686 kernel and the >>> results are the same again for the size of vmlinux. I then ran `objdump >>> --headers` and looked at the size of the .rodata section, where it's >>> also the same. I'm not quite sure what to make of this, as it's not what >>> I was expecting, but I think I tested it right. So maybe we're lucky >>> here? >> >> I tried a little harder to get _some_ difference on 32-bit, and >> managed to get one by doing i386_defconfig and then switching off >> modules to make all M into Y, and then compared sizes: >> >> vmlinux: 25590780 -> 25598972, so a 0.032% increase. >> bzImage: 8698944 -> 8699424, so a 0.0055% increase. >> >> So it does increase, ever so slightly, but a) on 32-bit, and b) a >> super, super tiny amount. >> >> In other words, I still think this patch is very much a-okay. But very >> eager to hear from Rafael on the approach. > > Increasing the ACPI_ID_LEN value is fine with me, but the patch > changelog is not entirely accurate. > > The ACPI subsystem uses struct acpi_device_id mostly (if not only) for > device ID matching and it is generally used for creating lists of ACPI > device IDs in drivers (and allow/deny lists etc). The device IDs > extracted from the ACPI tables can be longer than ACPI_ID_LEN. > > This means that drivers cannot match device IDs longer than 8 > characters (excluding the terminating 0), because the IDs in the lists > used by them for ID matching cannot be longer than this and not > because the ACPI subsystem is limited by that value. >
