usb: xhci: simplify Isochronous Scheduling Threshold handling

The IST is represented by bits 2:0, with bit 3 indicating the unit of
measurement, Frames or Microframes. Introduce xhci_ist_microframes(),
which returns the IST value in Microframes, simplifying the code and
reducing duplication.

Improve documentation in xhci-caps.h to clarify the IST register specifics,
including the unit conversion details. These change removes the need to
explain it each time the IST values is retrieved.

Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20251119142417.2820519-20-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-caps.h b/drivers/usb/host/xhci-caps.h
index 8a435786f950f659d3dd52d426cc106beb5fabeb..e772d5f30d3691c259b3a8fb8e70d92b31fcbd53 100644 (file)
--- a/drivers/usb/host/xhci-caps.h
+++ b/drivers/usb/host/xhci-caps.h
@@ -24,8 +24,15 @@
 /*
  * bits 3:0 - Isochronous Scheduling Threshold, frames or uframes that SW
  * needs to queue transactions ahead of the HW to meet periodic deadlines.
+ * - Bits 2:0: Threshold value
+ * - Bit 3: Unit indicator
+ *   - '1': Threshold in Frames
+ *   - '0': Threshold in Microframes (uframes)
+ * Note: 1 Frame = 8 Microframes
+ * xHCI specification section 5.3.4.
  */
-#define HCS_IST(p)             (((p) >> 0) & 0xf)
+#define HCS_IST_VALUE(p)       ((p) & 0x7)
+#define HCS_IST_UNIT(p)                ((p) & (1 << 3))
 /* bits 7:4 - Event Ring Segment Table Max, 2^(n) */
 #define HCS_ERST_MAX(p)                (((p) >> 4) & 0xf)
 /* bits 20:8 - Rsvd */

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 0ac7f9870d3d4368b354d694fbd5ace9a8c6bb70..104fd6f832658888bfe47448cd00ae352d03398b 100644 (file)
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3961,6 +3961,16 @@ static unsigned int xhci_get_last_burst_packet_count(struct xhci_hcd *xhci,
        return total_packet_count - 1;
 }
 
+/* Returns the Isochronous Scheduling Threshold in Microframes. 1 Frame is 8 Microframes. */
+static int xhci_ist_microframes(struct xhci_hcd *xhci)
+{
+       int ist = HCS_IST_VALUE(xhci->hcs_params2);
+
+       if (HCS_IST_UNIT(xhci->hcs_params2))
+               ist *= 8;
+       return ist;
+}
+
 /*
  * Calculates Frame ID field of the isochronous TRB identifies the
  * target frame that the Interval associated with this Isochronous
@@ -3980,17 +3990,7 @@ static int xhci_get_isoc_frame_id(struct xhci_hcd *xhci,
        else
                start_frame = (urb->start_frame + index * urb->interval) >> 3;
 
-       /* Isochronous Scheduling Threshold (IST, bits 0~3 in HCSPARAMS2):
-        *
-        * If bit [3] of IST is cleared to '0', software can add a TRB no
-        * later than IST[2:0] Microframes before that TRB is scheduled to
-        * be executed.
-        * If bit [3] of IST is set to '1', software can add a TRB no later
-        * than IST[2:0] Frames before that TRB is scheduled to be executed.
-        */
-       ist = HCS_IST(xhci->hcs_params2) & 0x7;
-       if (HCS_IST(xhci->hcs_params2) & (1 << 3))
-               ist <<= 3;
+       ist = xhci_ist_microframes(xhci);
 
        /* Software shall not schedule an Isoch TD with a Frame ID value that
         * is less than the Start Frame ID or greater than the End Frame ID,
@@ -4311,9 +4311,7 @@ int xhci_queue_isoc_tx_prepare(struct xhci_hcd *xhci, gfp_t mem_flags,
         * Round up to the next frame and consider the time before trb really
         * gets scheduled by hardare.
         */
-       ist = HCS_IST(xhci->hcs_params2) & 0x7;
-       if (HCS_IST(xhci->hcs_params2) & (1 << 3))
-               ist <<= 3;
+       ist = xhci_ist_microframes(xhci);
        start_frame += ist + XHCI_CFC_DELAY;
        start_frame = roundup(start_frame, 8);