linux-kernel - Re: [v10,2/2] PCI: Rockchip: Add Rockchip PCIe controller support

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Date:   Fri, 2 Sep 2016 10:44:09 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Shawn Lin <shawn.lin@...k-chips.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>, linux-pci@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Doug Anderson <dianders@...omium.org>,
        Wenrui Li <wenrui.li@...k-chips.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [v10,2/2] PCI: Rockchip: Add Rockchip PCIe controller support

On Thu, Sep 01, 2016 at 12:48:52PM -0500, Bjorn Helgaas wrote:
> On Thu, Sep 01, 2016 at 10:14:01AM -0700, Brian Norris wrote:

> > The use of HIWORD_UPDATE can indeed be a bit confusing, IMO, but this is
> > really a common Rockchip-ism that, once you read several of their
> > drivers, can make a little more sense. If you grep around, it's in at
> > least their clock, ethernet, SDHCI, PHY, and DP/DRM drivers. I might
> > defer to Heiko (upstream maintainer of Rockchip code) for a decision.
> > Maybe there's some intermediate ground where we keep the HIWORK_UPDATE()
> > logic (it does make sure we get the 16-bit shift right, I think) while
> > still refactoring a few other bits (like PCIE_CLIENT_CONF_LANE_NUM() and
> > PCIE_CLIENT_GEN_SEL() for wrapping HIWORK_UPDATE()?).

Here's a second proposal.  It retains HIWORD_UPDATE (though the structure
is different) so grep finds it along with the other Rockchip ones.

I'll post updated actual patches; this is just to give the idea:

-/*
-  * The higher 16-bit of this register is used for write protection
-  * only if BIT(x + 16) set to 1 the BIT(x) can be written.
-  */
-#define HIWORD_UPDATE(val, mask, shift) \
-	((val) << (shift) | (mask) << ((shift) + 16))

-#define PCIE_CLIENT_CONF_ENABLE			BIT(0)
-#define PCIE_CLIENT_CONF_ENABLE_SHIFT		0
-#define PCIE_CLIENT_CONF_ENABLE_MASK		0x1
-#define PCIE_CLIENT_LINK_TRAIN_ENABLE		1
-#define PCIE_CLIENT_LINK_TRAIN_SHIFT		1
-#define PCIE_CLIENT_LINK_TRAIN_MASK		0x1
-#define PCIE_CLIENT_ARI_ENABLE			BIT(0)
-#define PCIE_CLIENT_ARI_ENABLE_SHIFT		3
-#define PCIE_CLIENT_ARI_ENABLE_MASK		0x1
-#define PCIE_CLIENT_CONF_LANE_NUM(x)		(x / 2)
-#define PCIE_CLIENT_CONF_LANE_NUM_SHIFT		4
-#define PCIE_CLIENT_CONF_LANE_NUM_MASK		0x3
-#define PCIE_CLIENT_MODE_RC			BIT(0)
-#define PCIE_CLIENT_MODE_SHIFT			6
-#define PCIE_CLIENT_MODE_MASK			0x1
-#define PCIE_CLIENT_GEN_SEL_2			1
-#define PCIE_CLIENT_GEN_SEL_SHIFT		7
-#define PCIE_CLIENT_GEN_SEL_MASK		0x1

+/*
+ * The upper 16 bits of the PCIE_CLIENT registers are a write mask for the
+ * lower 16 bits.  This allows atomic updates of the register without
+ * locking.
+ */
+#define HIWORD_UPDATE(mask, val)	((mask << 16) | val)
+
+#define ENCODE_LANES(x)			(((x >> 1) & 3) << 4)
+
+#define PCIE_CLIENT_CONF_ENABLE		HIWORD_UPDATE(0x0001, 0x0001)
+#define PCIE_CLIENT_LINK_TRAIN_ENABLE	HIWORD_UPDATE(0x0002, 0x0002)
+#define PCIE_CLIENT_CONF_LANE_NUM(x)	HIWORD_UPDATE(0x0030, ENCODE_LANES(x))
+#define PCIE_CLIENT_GEN_SEL_2		HIWORD_UPDATE(0x0040, 0x0040)

 	rockchip_pcie_write(rockchip,
-		   HIWORD_UPDATE(PCIE_CLIENT_CONF_ENABLE,
-				 PCIE_CLIENT_CONF_ENABLE_MASK,
-				 PCIE_CLIENT_CONF_ENABLE_SHIFT) |
-		   HIWORD_UPDATE(PCIE_CLIENT_CONF_LANE_NUM(rockchip->lanes),
-				 PCIE_CLIENT_CONF_LANE_NUM_MASK,
-				 PCIE_CLIENT_CONF_LANE_NUM_SHIFT) |
-		   HIWORD_UPDATE(PCIE_CLIENT_MODE_RC,
-				 PCIE_CLIENT_MODE_MASK,
-				 PCIE_CLIENT_MODE_SHIFT) |
-		   HIWORD_UPDATE(PCIE_CLIENT_ARI_ENABLE,
-				 PCIE_CLIENT_ARI_ENABLE_MASK,
-				 PCIE_CLIENT_ARI_ENABLE_SHIFT) |
-		   HIWORD_UPDATE(PCIE_CLIENT_GEN_SEL_2,
-				 PCIE_CLIENT_GEN_SEL_MASK,
-				 PCIE_CLIENT_GEN_SEL_SHIFT),
-		   PCIE_CLIENT_BASE);
+			    PCIE_CLIENT_CONF_ENABLE |
+			    PCIE_CLIENT_LINK_TRAIN_ENABLE |
+			    PCIE_CLIENT_ARI_ENABLE |
+			    PCIE_CLIENT_CONF_LANE_NUM(rockchip->lanes) |
+			    PCIE_CLIENT_MODE_RC |
+			    PCIE_CLIENT_GEN_SEL_2,
+				PCIE_CLIENT_BASE);