linux-kernel - Why does cdns_pcie_ep_set_bar use sz > SZ_2G for is

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Date:   Wed, 19 Jan 2022 09:27:44 +0000
From:   Li Chen <lchen@...arella.com>
To:     Tom Joseph <tjoseph@...ence.com>
CC:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Why does cdns_pcie_ep_set_bar use sz > SZ_2G for is_64bits in
 pcie-cadence-ep.c?

Hi, Tom

>From these function:
static int cdns_pcie_ep_set_bar(struct pci_epc *epc, u8 fn, u8 vfn,
				struct pci_epf_bar *epf_bar)
{
	......
	if ((flags & PCI_BASE_ADDRESS_SPACE) == PCI_BASE_ADDRESS_SPACE_IO) {
		ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_IO_32BITS;
	} else {
		bool is_prefetch = !!(flags & PCI_BASE_ADDRESS_MEM_PREFETCH);
		bool is_64bits = sz > SZ_2G;
		if (is_64bits && (bar & 1))
			return -EINVAL;
		if (is_64bits && !(flags & PCI_BASE_ADDRESS_MEM_TYPE_64))
			epf_bar->flags |= PCI_BASE_ADDRESS_MEM_TYPE_64;

		if (is_64bits && is_prefetch)
			ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_PREFETCH_MEM_64BITS;
		else if (is_prefetch)
			ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_PREFETCH_MEM_32BITS;
		else if (is_64bits)
			ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_MEM_64BITS;
		else
			ctrl = CDNS_PCIE_LM_BAR_CFG_CTRL_MEM_32BITS;
	}

	......
}

I don't understand why should sz > SZ_2G be taken into account for 64_bits. From my personal practice, there is no problem to use CDNS_PCIE_LM_BAR_CFG_CTRL_MEM_64BITS or CDNS_PCIE_LM_BAR_CFG_CTRL_PREFETCH_MEM_64BITS when sz < SZ_2G.

Regards,
Li

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