[PATCH 1/2] usb: xhci: improve HCD page size validation and setting

[Niklas Neronin <niklas.neronin@linux.intel.com>]

xHC supports a page size of (2^(n+12)), where 'n' is the Page Size Bit.
The page size of 4096 bytes is common and always supported. Consequently,
the xHCI driver always sets the 'page_size' to 4096 (i.e., (1 << 12)).

At present, the xHCI driver reads the Page Size register but does not use
the value, except for printing a two useless debug traces. This introduces
unnecessary code into xhci_mem_init(), which is already quite large.
Although the page size is not currently modified, it may be in the future.

To balance both current and future needs, the page size setting code is
moved to a separate function. This rework ensures that the Page Size
register is not read for the minimum value (4096). However, if a different
value is provided, it will not be ignored, rather clamped between the
valid min and max page size.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
---
 drivers/usb/host/xhci-mem.c | 40 ++++++++++++++++++++++---------------
 drivers/usb/host/xhci.h     |  9 ++++++---
 2 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index d2900197a49e..8a6b91862cae 100644
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -1959,7 +1959,6 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci)
 	xhci->interrupters = NULL;
 
 	xhci->page_size = 0;
-	xhci->page_shift = 0;
 	xhci->usb2_rhub.bus_state.bus_suspended = 0;
 	xhci->usb3_rhub.bus_state.bus_suspended = 0;
 }
@@ -2378,6 +2377,27 @@ xhci_create_secondary_interrupter(struct usb_hcd *hcd, unsigned int segs,
 }
 EXPORT_SYMBOL_GPL(xhci_create_secondary_interrupter);
 
+static void xhci_hcd_page_size(struct xhci_hcd *xhci)
+{
+	u32 page_size;
+
+	if (xhci->page_size <= HCD_PAGE_MIN) {
+		xhci->page_size = HCD_PAGE_MIN;
+	} else {
+		/* Max page size is 2^(n+12), where 'n' is the first 15:0 bit set */
+		page_size = readl(&xhci->op_regs->page_size) & HCD_PAGE_SIZE_MASK;
+		page_size = 1 << (ffs(page_size) + 12);
+
+		if (page_size < xhci->page_size)
+			xhci->page_size = page_size;
+		else
+			xhci->page_size = (1 << ffs(xhci->page_size));
+	}
+
+	xhci_dbg_trace(xhci, trace_xhci_dbg_init, "HCD page size set to %iK",
+		       xhci->page_size / 1024);
+}
+
 int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
 {
 	struct xhci_interrupter *ir;
@@ -2385,7 +2405,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
 	dma_addr_t	dma;
 	unsigned int	val, val2;
 	u64		val_64;
-	u32		page_size, temp;
+	u32		temp;
 	int		i;
 
 	INIT_LIST_HEAD(&xhci->cmd_list);
@@ -2394,20 +2414,8 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
 	INIT_DELAYED_WORK(&xhci->cmd_timer, xhci_handle_command_timeout);
 	init_completion(&xhci->cmd_ring_stop_completion);
 
-	page_size = readl(&xhci->op_regs->page_size);
-	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
-			"Supported page size register = 0x%x", page_size);
-	i = ffs(page_size);
-	if (i < 16)
-		xhci_dbg_trace(xhci, trace_xhci_dbg_init,
-			"Supported page size of %iK", (1 << (i+12)) / 1024);
-	else
-		xhci_warn(xhci, "WARN: no supported page size\n");
-	/* Use 4K pages, since that's common and the minimum the HC supports */
-	xhci->page_shift = 12;
-	xhci->page_size = 1 << xhci->page_shift;
-	xhci_dbg_trace(xhci, trace_xhci_dbg_init,
-			"HCD page size set to %iK", xhci->page_size / 1024);
+	/* If 'page_size' is not set, use 4K pages, since that's common and always supported */
+	xhci_hcd_page_size(xhci);
 
 	/*
 	 * Program the Number of Device Slots Enabled field in the CONFIG
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index f0fb696d5619..f998df70f80f 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -211,6 +211,11 @@ struct xhci_op_regs {
 #define CONFIG_CIE		(1 << 9)
 /* bits 10:31 - reserved and should be preserved */
 
+/* bits 15:0 - HCD page shift bit */
+#define HCD_PAGE_SIZE_MASK      0xffff
+/* HCD page size 4KB up to 128MB, Rev 1.2 Section 5.4.3. */
+#define HCD_PAGE_MIN            (1 << 12)
+
 /**
  * struct xhci_intr_reg - Interrupt Register Set
  * @irq_pending:	IMAN - Interrupt Management Register.  Used to enable
@@ -1502,10 +1507,8 @@ struct xhci_hcd {
 	u16		max_interrupters;
 	/* imod_interval in ns (I * 250ns) */
 	u32		imod_interval;
-	/* 4KB min, 128MB max */
+	/* Always set to HCD_PAGE_MIN (4KB) */
 	int		page_size;
-	/* Valid values are 12 to 20, inclusive */
-	int		page_shift;
 	/* MSI-X/MSI vectors */
 	int		nvecs;
 	/* optional clocks */
-- 
2.45.2