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usb: xhci: simplify Isochronous Scheduling Threshold handling

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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>
This commit is contained in:
Niklas Neronin
2025-11-19 16:24:13 +02:00
committed by Greg Kroah-Hartman
parent edab00902b
commit f724e34719
2 changed files with 20 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
drivers/usb/host/xhci-caps.h
View File

@@ -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 */

26
drivers/usb/host/xhci-ring.c
View File

@@ -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);