usb: xhci: cleanup IMOD register comments

Patch does not contain any functional changes.

Add missing macro descriptions with specific bit definitions for each data
field and reordered them accordingly.

Remove "HW use only" from Interrupt Moderation Counter. xHCI Specification
1.2, section 5.5.2.2, states "This counter may be directly written by
software at any time to alter the interrupt rate."

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250515135621.335595-21-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 7865e21f0b1f186d8777447ea878ce82800066d0..4a4ce6784bf079d0abc3b8c520786be38d5184ae 100644 (file)
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -210,14 +210,13 @@ struct xhci_op_regs {
 #define XHCI_PAGE_SIZE_MASK     0xffff
 
 /**
- * struct xhci_intr_reg - Interrupt Register Set
- * @irq_pending:       IMAN - Interrupt Management Register.  Used to enable
+ * struct xhci_intr_reg - Interrupt Register Set, v1.2 section 5.5.2.
+ * @irq_pending:       IMAN - Interrupt Management Register. Used to enable
  *                     interrupts and check for pending interrupts.
- * @irq_control:       IMOD - Interrupt Moderation Register.
- *                     Used to throttle interrupts.
- * @erst_size:         Number of segments in the Event Ring Segment Table (ERST).
- * @erst_base:         ERST base address.
- * @erst_dequeue:      Event ring dequeue pointer.
+ * @irq_control:       IMOD - Interrupt Moderation Register. Used to throttle interrupts.
+ * @erst_size:         ERSTSZ - Number of segments in the Event Ring Segment Table (ERST).
+ * @erst_base:         ERSTBA - Event ring segment table base address.
+ * @erst_dequeue:      ERDP - Event ring dequeue pointer.
  *
  * Each interrupter (defined by a MSI-X vector) has an event ring and an Event
  * Ring Segment Table (ERST) associated with it.  The event ring is comprised of
@@ -242,12 +241,13 @@ struct xhci_intr_reg {
 #define        IMAN_IE                 (1 << 1)
 
 /* irq_control bitmasks */
-/* Minimum interval between interrupts (in 250ns intervals).  The interval
- * between interrupts will be longer if there are no events on the event ring.
- * Default is 4000 (1 ms).
+/*
+ * bits 15:0 - Interrupt Moderation Interval, the minimum interval between interrupts
+ * (in 250ns intervals). The interval between interrupts will be longer if there are no
+ * events on the event ring. Default is 4000 (1 ms).
  */
 #define ER_IRQ_INTERVAL_MASK   (0xffff)
-/* Counter used to count down the time to the next interrupt - HW use only */
+/* bits 31:16 - Interrupt Moderation Counter, used to count down the time to the next interrupt */
 #define ER_IRQ_COUNTER_MASK    (0xffff << 16)
 
 /* erst_size bitmasks */
@@ -259,15 +259,18 @@ struct xhci_intr_reg {
 #define ERST_BASE_ADDRESS_MASK GENMASK_ULL(63, 6)
 
 /* erst_dequeue bitmasks */
-/* Dequeue ERST Segment Index (DESI) - Segment number (or alias)
- * where the current dequeue pointer lies.  This is an optional HW hint.
+/*
+ * bits 2:0 - Dequeue ERST Segment Index (DESI), is the segment number (or alias) where the
+ * current dequeue pointer lies. This is an optional HW hint.
  */
 #define ERST_DESI_MASK         (0x7)
-/* Event Handler Busy (EHB) - is the event ring scheduled to be serviced by
+/*
+ * bit 3 - Event Handler Busy (EHB), whether the event ring is scheduled to be serviced by
  * a work queue (or delayed service routine)?
  */
 #define ERST_EHB               (1 << 3)
-#define ERST_PTR_MASK          (GENMASK_ULL(63, 4))
+/* bits 63:4 - Event Ring Dequeue Pointer */
+#define ERST_PTR_MASK          GENMASK_ULL(63, 4)
 
 /**
  * struct xhci_run_regs