Re: [PATCH v8 1/4] firmware: introduce sysfs driver for QEMU's fw_cfg device

On Sun, Feb 21, 2016 at 08:06:17AM -0500, Gabriel L. Somlo wrote:

quoted

quoted

+static void fw_cfg_io_cleanup(void)
+{
+	if (fw_cfg_is_mmio) {
+		iounmap(fw_cfg_dev_base);
+		release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+	} else {
+		ioport_unmap(fw_cfg_dev_base);
+		release_region(fw_cfg_p_base, fw_cfg_p_size);
+	}
+}
+
+/* arch-specific ctrl & data register offsets are not available in ACPI, DT */

So for all arches which support ACPI, I think this driver
should just rely on ACPI.

There was a discussion about that a few versions ago, and IIRC the
conclusion was not to expect the firmware to contend for fw_cfg access
after the guest kernel boots:

https://lkml.org/lkml/2015/10/5/283

So it looks like NVDIMM at least wants to pass label data to guest -
for which fw cfg might be a reasonable choice.

I suspect things changed - fw cfg used to be very slow but we now have
DMA interface which makes it useful for a range of applications.

(I even had a prototype version doing what you suggested, but per the above
reference decided to drop it -- which IMHO is for the better, since otherwise
I'd have had to ifdef between ACPI and non-ACPI versions of the driver --
see https://lkml.org/lkml/2015/11/4/534 )

I'm not sure why you have these ifdefs - they are on the host, are they
not?

-- 
MST