On 08/05/2020 12:44, Jiaxun Yang wrote:

Replying to an old mail ...

range->fwnode = &of_root->fwnode;
+	range->size = MMIO_LOWER_RESERVED;
+	range->hw_start = LOONGSON_PCIIO_BASE;
+	range->flags = LOGIC_PIO_CPU_MMIO;
+
+	if (logic_pio_register_range(range)) {
+		pr_err("Failed to reserve PIO range for legacy ISA\n");
+		goto free_range;
+	}

Hi Jiaxun,

+
+	if (WARN(range->io_start != 0,
+			"Reserved PIO range does not start from 0\n"))

Do the mips code still rely on this check?

I was considering changing the logical PIO code to reserve the first 64K 
of PCI MMIO space, but making that change would break this code as 
things stand.

The motivation is that some drivers, like [0], access IO ports 
unconditionally and can kill systems when no PCI host exists. By 
reserving the first 64K, accesses by those drivers could nullified.

Thanks,
John

[0] 
https://lore.kernel.org/linux-input/20210112055129.7840-1-song.bao.hua@hisilicon.com/T/#t (local)

+		goto unregister;
+
+	/*
+	 * i8259 would access I/O space, so mapping must be done here.
+	 * Please remove it when all drivers can be managed by logic_pio.
+	 */
+	ioremap_page_range(PCI_IO_START, PCI_IO_START + MMIO_LOWER_RESERVED,
+				LOONGSON_PCIIO_BASE,
+				pgprot_device(PAGE_KERNEL));
+
+	return;
+unregister: