[PATCH v2 08/13] usb: xhci: simplify Isochronous Scheduling Threshold handling
From: Niklas Neronin <hidden>
Date: 2025-11-13 12:59:02
Subsystem:
the rest, usb subsystem, usb xhci driver · Maintainers:
Linus Torvalds, Greg Kroah-Hartman, Mathias Nyman
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 <redacted> --- v2: * Change xhci_ist_in_microseconds() argument to 'xhci'. * Rename xhci_ist_in_microseconds() to xhci_ist_microframes(). drivers/usb/host/xhci-caps.h | 9 ++++++++- drivers/usb/host/xhci-ring.c | 26 ++++++++++++-------------- 2 files changed, 20 insertions(+), 15 deletions(-)
diff --git a/drivers/usb/host/xhci-caps.h b/drivers/usb/host/xhci-caps.h
index 8a435786f950..e772d5f30d36 100644
--- 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 5f46661c8e6b..6ea0ae27617e 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c@@ -3983,6 +3983,16 @@ 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
@@ -4002,17 +4012,7 @@ 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,
@@ -4333,9 +4333,7 @@ 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);
--
2.50.1