Duc, Aleksey, all, I have a question about this... On 12/05/2016 01:51 PM, Duc Dang wrote: > On Mon, Dec 5, 2016 at 5:05 AM, Aleksey Makarov > <aleksey.makarov@xxxxxxxxxx> wrote: >> Check the 'Register Bit Width' field of the ACPI Generic Address >> Structure that specifies the address of the UART registers to >> decide if the driver should use "mmio32" access instead of "mmio". >> >> If the driver is other than 16550 the access with is defined >> by the Interface Type field of the SPCR table. I have two questions about this: 1). Why is this not a full 16550 (ACPI_DBG2_16550_COMPATIBLE)? 2). Why is it a ACPI_DBG2_16550_SUBSET you are assuming here? The SPCR and DBG2 spec clearly state that the _SUBSET is intended to represent a UART compatible with the earlier DGBP specification, not that a UART is a "subset" of a full 16550 (which seems to be the assumption in this patch). It's important we get this right. I built a test kernel with this patch and updated ACPI tables earlier, but it didn't boot with a console because I had left it a subtype 0, but just changed the width to 32 bit, which is what I expected. Further, I've heard back from Microsoft and they're looking at adding a specific subtype for this. If they do, I'm inclined to address existing designs with your patch (but I would favor this check because against the full 16550) and then switch newer APM based designs to the new subtype. Jon. -- Computer Architect | Sent from my Fedora powered laptop -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
