Re: [PATCH 3/3] usb: xhci: allocate internal DCBAA mirror dynamically
From: Michal Pecio <hidden>
Date: 2026-05-20 22:08:55
On Thu, 7 May 2026 10:39:45 +0200, Niklas Neronin wrote:
Allocate the internal virtual device array dynamically based on the maximum number of slots reported by the host controller. Previously, the array was always allocated to the absolute maximum of 255 entries. Repurpose the 'MAX_HC_SLOTS' macro to limit the number of enabled slots. This mirrors how the maximum number of ports and interrupters are handled. The allocation now uses kcalloc_node(), which zeroes the memory automatically, making the explicit memset() call unnecessary. Signed-off-by: Niklas Neronin <redacted>
Hi, The series looks alright, but a few small comments below:
quoted hunk ↗ jump to hunk
--- drivers/usb/host/xhci-mem.c | 14 ++++++++++++-- drivers/usb/host/xhci.c | 4 +--- drivers/usb/host/xhci.h | 9 ++++++--- 3 files changed, 19 insertions(+), 8 deletions(-)diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c index ac915dacd886..1effc9f08678 100644 --- a/drivers/usb/host/xhci-mem.c +++ b/drivers/usb/host/xhci-mem.c@@ -1953,8 +1953,11 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci) xhci_dbg_trace(xhci, trace_xhci_dbg_init, "Freed command ring"); xhci_cleanup_command_queue(xhci); - for (i = xhci->max_slots; i > 0; i--) - xhci_free_virt_devices_depth_first(xhci, i); + if (xhci->devs) { + for (i = xhci->max_slots; i > 0; i--) + xhci_free_virt_devices_depth_first(xhci, i); + kfree(xhci->devs); + } dma_pool_destroy(xhci->segment_pool); xhci->segment_pool = NULL;@@ -2011,6 +2014,7 @@ void xhci_mem_cleanup(struct xhci_hcd *xhci) xhci->rh_bw = NULL; xhci->port_caps = NULL; xhci->interrupters = NULL; + xhci->devs = NULL; xhci->usb2_rhub.bus_state.bus_suspended = 0; xhci->usb3_rhub.bus_state.bus_suspended = 0;@@ -2417,6 +2421,12 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags) xhci_dbg_trace(xhci, trace_xhci_dbg_init, "Starting %s", __func__); + xhci_dbg_trace(xhci, trace_xhci_dbg_init, "Allocating internal virtual device array");
I don't think this is useful in any way. One look at the code makes it clear that this is going to happen each time this function is called.
quoted hunk ↗ jump to hunk
+ xhci->devs = kcalloc_node(xhci->max_slots + 1, sizeof(*xhci->devs), flags, + dev_to_node(dev)); + if (!xhci->devs) + goto fail; + xhci->dcbaa.ctx_array = dma_alloc_coherent(dev, array_size(sizeof(*dcbaa->ctx_array), xhci->max_slots + 1), &dcbaa->dma, flags);diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c index 9a471bd72265..151a759806f8 100644 --- a/drivers/usb/host/xhci.c +++ b/drivers/usb/host/xhci.c@@ -5460,7 +5460,7 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks) if (xhci->hci_version > 0x100) xhci->hcc_params2 = readl(&xhci->cap_regs->hcc_params2); - xhci->max_slots = HCS_MAX_SLOTS(hcs_params1); + xhci->max_slots = min(HCS_MAX_SLOTS(hcs_params1), MAX_HC_SLOTS);
HCSPARAMS1.MaxSlots is 8 bits wide, so it will never exceed 255. There is no need to add this check. And the macro seems to porperly mask out excess bits picked up from other fields, so no worries about that either. And if it didn't, it should be fixed instead of (wrongly) assuming 255 slots.
quoted hunk ↗ jump to hunk
xhci->max_ports = min(HCS_MAX_PORTS(hcs_params1), MAX_HC_PORTS); /* xhci-plat or xhci-pci might have set max_interrupters already */ if (!xhci->max_interrupters)@@ -5533,8 +5533,6 @@ int xhci_gen_setup(struct usb_hcd *hcd, xhci_get_quirks_t get_quirks) init_completion(&xhci->cmd_ring_stop_completion); xhci_hcd_page_size(xhci); - memset(xhci->devs, 0, MAX_HC_SLOTS * sizeof(*xhci->devs)); - /* Allocate xHCI data structures */ retval = xhci_mem_init(xhci, GFP_KERNEL); if (retval)diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h index b467b875eeba..f977c8e6a90a 100644 --- a/drivers/usb/host/xhci.h +++ b/drivers/usb/host/xhci.h@@ -33,8 +33,11 @@ /* xHCI PCI Configuration Registers */ #define XHCI_SBRN_OFFSET (0x60) -/* Max number of USB devices for any host controller - limit in section 6.1 */ -#define MAX_HC_SLOTS 256 +/* + * Max number of Devices Slots. xHCI specification section 5.3.3 + * Valid values are in the range of 1 to 255. + */ +#define MAX_HC_SLOTS 255
Then if there are no other uses, this constant can simply be removed.
quoted hunk ↗ jump to hunk
/* * Max Number of Ports. xHCI specification section 5.3.3 * Valid values are in the range of 1 to 255.@@ -1552,7 +1555,7 @@ struct xhci_hcd { /* these are not thread safe so use mutex */ struct mutex mutex; /* Internal mirror of the HW's dcbaa */ - struct xhci_virt_device *devs[MAX_HC_SLOTS]; + struct xhci_virt_device **devs; /* For keeping track of bandwidth domains per roothub. */ struct xhci_root_port_bw_info *rh_bw;-- 2.50.1