can: gs_usb: increase max interface to U8_MAX

This issue was found by Runcheng Lu when develop HSCanT USB to CAN FD
converter[1]. The original developers may have only 3 interfaces
device to test so they write 3 here and wait for future change.

During the HSCanT development, we actually used 4 interfaces, so the
limitation of 3 is not enough now. But just increase one is not
future-proofed. Since the channel index type in gs_host_frame is u8,
just make canch[] become a flexible array with a u8 index, so it
naturally constraint by U8_MAX and avoid statically allocate 256
pointer for every gs_usb device.

[1]: https://github.com/cherry-embedded/HSCanT-hardware

Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
Reported-by: Runcheng Lu <runcheng.lu@hpmicro.com>
Cc: stable@vger.kernel.org
Reviewed-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
Link: https://patch.msgid.link/20250930-gs-usb-max-if-v5-1-863330bf6666@coelacanthus.name
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index c9482d6e947b0c7b033dc4f0c35f5b111e1bfd92..9fb4cbbd6d6dc88f433020eb0417ea53cd0c4d5f 100644 (file)
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -289,11 +289,6 @@ struct gs_host_frame {
 #define GS_MAX_RX_URBS 30
 #define GS_NAPI_WEIGHT 32
 
-/* Maximum number of interfaces the driver supports per device.
- * Current hardware only supports 3 interfaces. The future may vary.
- */
-#define GS_MAX_INTF 3
-
 struct gs_tx_context {
        struct gs_can *dev;
        unsigned int echo_id;
@@ -324,7 +319,6 @@ struct gs_can {
 
 /* usb interface struct */
 struct gs_usb {
-       struct gs_can *canch[GS_MAX_INTF];
        struct usb_anchor rx_submitted;
        struct usb_device *udev;
 
@@ -336,9 +330,11 @@ struct gs_usb {
 
        unsigned int hf_size_rx;
        u8 active_channels;
+       u8 channel_cnt;
 
        unsigned int pipe_in;
        unsigned int pipe_out;
+       struct gs_can *canch[] __counted_by(channel_cnt);
 };
 
 /* 'allocate' a tx context.
@@ -599,7 +595,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
        }
 
        /* device reports out of range channel id */
-       if (hf->channel >= GS_MAX_INTF)
+       if (hf->channel >= parent->channel_cnt)
                goto device_detach;
 
        dev = parent->canch[hf->channel];
@@ -699,7 +695,7 @@ resubmit_urb:
        /* USB failure take down all interfaces */
        if (rc == -ENODEV) {
 device_detach:
-               for (rc = 0; rc < GS_MAX_INTF; rc++) {
+               for (rc = 0; rc < parent->channel_cnt; rc++) {
                        if (parent->canch[rc])
                                netif_device_detach(parent->canch[rc]->netdev);
                }
@@ -1460,17 +1456,19 @@ static int gs_usb_probe(struct usb_interface *intf,
        icount = dconf.icount + 1;
        dev_info(&intf->dev, "Configuring for %u interfaces\n", icount);
 
-       if (icount > GS_MAX_INTF) {
+       if (icount > type_max(parent->channel_cnt)) {
                dev_err(&intf->dev,
                        "Driver cannot handle more that %u CAN interfaces\n",
-                       GS_MAX_INTF);
+                       type_max(parent->channel_cnt));
                return -EINVAL;
        }
 
-       parent = kzalloc(sizeof(*parent), GFP_KERNEL);
+       parent = kzalloc(struct_size(parent, canch, icount), GFP_KERNEL);
        if (!parent)
                return -ENOMEM;
 
+       parent->channel_cnt = icount;
+
        init_usb_anchor(&parent->rx_submitted);
 
        usb_set_intfdata(intf, parent);
@@ -1531,7 +1529,7 @@ static void gs_usb_disconnect(struct usb_interface *intf)
                return;
        }
 
-       for (i = 0; i < GS_MAX_INTF; i++)
+       for (i = 0; i < parent->channel_cnt; i++)
                if (parent->canch[i])
                        gs_destroy_candev(parent->canch[i]);