On Mon, May 8, 2017 at 3:57 PM, Loc Ho <lho@xxxxxxx> wrote: > Hi Jon, > >>> >>>>> The current SPCR code does not check the access width of the mmio, and >>>>> uses a default of 8bit register accesses. This prevents devices that >>>>> only do 16 or 32bit register accesses from working. By simply checking >>>>> this field and setting the mmio string appropriately, this issue can be >>>>> corrected. To prevent any legacy issues, the code will default to 8bit >>>>> accesses if the value is anything but 16 or 32. >>>> >>>> Thanks for this. Just as an FYI I've a running discussion with Microsoft >>>> about defining additional UART subtypes in the DBG2 for special case >>>> UARTs. Specifically, I want to address AppliedMicro's special 8250 dw IP >>>> that also has a non-standard clock. At this time, there is general >>>> agreement to use the access width for some cases rather than defining >>>> yet more subtypes - so your patch is good. >>>> >>>> Loc/Applied: please track this thread, incorporate feedback, and also >>>> track the other general recent discussions of 8250 dw from this week. >>> >>> Thanks for forward me this patch. This patch does not work with X-Gene >>> v1 and v2 SoC's. As BIOS SPCR encodes these info as: >>> >>> Bit Width: 32 >>> Bit Offset: 0 >>> Encoded Access Width: 01 (Byte Access) >>> >>> With this patch, it would use the "mmio" instead the "mmio32" as with >>> this patch - https://patchwork.kernel.org/patch/9460959 >> >> I think this is why we need the DBG2 subtype for Applied X-Gene1. I'm >> hoping the update to the SPCR/DBG2 spec is done soon. > > We can't rely on the BIOS change to support this new subtype as we > have system that is already in production deployment. When these > system upgrade to new version of the OS (stock, RHELSA, or whatever), > they will break. We need the patch from > https://patchwork.kernel.org/patch/9460959/ rolled upstream. There is no reason why the patch you reference cannot co-exist with the one I am submitting here. In this case, my patch would set it to mmio, then the patch you link above would reset it to mmio32. Personally, I would recommend a big, fat comment on why this extra step is necessary, but it should work as desired. Alternatively, we could add some kind of quirk library (similar to qdf2400_erratum_44_present) where the OEM/OEM Table ID is referenced and workaround applied. Thoughts? Thanks, Jon Mas(on) > > -Loc -- 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
