usb: xhci: limit number of interrupts to 128

The xHCI driver defines only 128 interrupter register slots, yet allows up
to 2047 interrupters. According to the xHCI specification, the maximum
valid number of interrupters is 1024. These mismatches can lead to
out-of-range accesses and excessive memory use.

The Number of Interrupters (MaxIntrs) field occupies bits 18:8 of the
HCSPARAMS1 register, which can yield a value up to 2047, although the
specification limits it to 1024. Cap the value using the 'MAX_HC_INTRS'
macro.

Set 'xhci->max_intrs' to the minimum of the value reported by the
HCSPARAMS1 register and 'MAX_HC_INTRS'. The interrupter register slot
array is defined for 1024 entries, serving only as a structural template
and not increasing memory usage.

Although the xHCI specification allows up to 1024 interrupters, raising
'MAX_HC_INTRS' above 128 provides no practical benefit. The driver only
uses the primary interrupter (0), and secondary interrupters (1+) are
rarely, if ever, used in practice. No reports exist of usage beyond 128.
Therefore, I have limited it to 128.

Summary:
 * Interrupter allocations are now limited to 128 from 2047.
 * Interrupter Register template slots are set to 1024 from 128.
 * Macro 'MAX_HC_INTRS' can be modified to set the interrupter limit.

==== Detailed interrupter explanation ====

There are two relevant components:

Interrupter array:
This holds the software interrupter structures and is allocated by the
xhci driver. The number of interrupters allocated is determined by the
HCSPARAMS1 register field, which specifies the supported interrupter
count.

Interrupter register slots:
This is a template struct used to access the hardware's runtime
registers. It is not allocated by the driver, the hardware defines and
owns this memory region, and the driver only maps it for MMIO access.

Each entry in the interrupter array points to its corresponding
interrupter register slot in the hardware region once that interrupter
is enabled.

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/20251119142417.2820519-18-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

0 files changed, 0 insertions, 0 deletions