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[PATCH v2 06/15] Add comment about why 32-bit read/modify/write isn't safe.

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  [PATCH v2 06/15] Add comment about why 32-bit read/modify/write  isn't safe. Bjorn Helgaas <bhelgaas@google.com> - 2016-09-02 18:00 +0200

#1475278 — [PATCH v2 06/15] Add comment about why 32-bit read/modify/write isn't safe.

---
 drivers/pci/host/pcie-rockchip.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pci/host/pcie-rockchip.c b/drivers/pci/host/pcie-rockchip.c
index ea75f35..c0c3ad5 100644
--- a/drivers/pci/host/pcie-rockchip.c
+++ b/drivers/pci/host/pcie-rockchip.c
@@ -282,6 +282,11 @@ static int rockchip_pcie_wr_own_conf(struct rockchip_pcie *rockchip,
 
 	mask = ~(((1 << (size * 8)) - 1) << ((where & 0x3) * 8));
 
+	/*
+	 * N.B. This read/modify/write isn't safe in general because it can
+	 * corrupt RW1C bits in adjacent registers.  But the hardware
+	 * doesn't support smaller writes.
+	 */
 	tmp = readl(rockchip->apb_base + PCIE_RC_CONFIG_BASE + offset) & mask;
 	tmp |= val << ((where & 0x3) * 8);
 	writel(tmp, rockchip->apb_base + PCIE_RC_CONFIG_BASE + offset);

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