usb: uhci: Work around bogus clang shift overflow warning from DMA_BIT_MASK(64)

After commit 18a9ec886d32 ("usb: uhci: Add Aspeed AST2700 support"),
clang incorrectly warns:

  In file included from drivers/usb/host/uhci-hcd.c:855:
  drivers/usb/host/uhci-platform.c:69:32: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
     69 | static const u64 dma_mask_64 = DMA_BIT_MASK(64);
        |                                ^~~~~~~~~~~~~~~~
  include/linux/dma-mapping.h:93:54: note: expanded from macro 'DMA_BIT_MASK'
     93 | #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
        |                                                      ^ ~~~

clang has a long outstanding and complicated problem [1] with generating
a proper control flow graph at global scope, resulting in it being
unable to understand that this shift can never happen due to the
'n == 64' check.

Restructure the code to only use DMA_BIT_MASK() within
uhci_hcd_platform_probe() (i.e., function scope) to avoid this global
scope issue, similar to the approach of commit 274f2232a94f ("usb: ehci:
Add Aspeed AST2700 support").

Closes: https://github.com/ClangBuiltLinux/linux/issues/2136
Link: https://github.com/ClangBuiltLinux/linux/issues/92
Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Ryan Chen <ryan_chen@aspeedtech.com>
Link: https://patch.msgid.link/20251015-usb-uhci-avoid-bogus-clang-shift-warning-v2-1-68532d2f6114@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/uhci-platform.c b/drivers/usb/host/uhci-platform.c
index 37607f985cc012a5b947294373bf6c348f70e6da..5e02f2ceafb6eeff4b33cf7f42eecf8a5ce573ae 100644 (file)
--- a/drivers/usb/host/uhci-platform.c
+++ b/drivers/usb/host/uhci-platform.c
@@ -65,13 +65,10 @@ static const struct hc_driver uhci_platform_hc_driver = {
        .hub_control =          uhci_hub_control,
 };
 
-static const u64 dma_mask_32 = DMA_BIT_MASK(32);
-static const u64 dma_mask_64 = DMA_BIT_MASK(64);
-
 static int uhci_hcd_platform_probe(struct platform_device *pdev)
 {
        struct device_node *np = pdev->dev.of_node;
-       const u64 *dma_mask_ptr;
+       bool dma_mask_64 = false;
        struct usb_hcd *hcd;
        struct uhci_hcd *uhci;
        struct resource *res;
@@ -85,11 +82,11 @@ static int uhci_hcd_platform_probe(struct platform_device *pdev)
         * Since shared usb code relies on it, set it here for now.
         * Once we have dma capability bindings this can go away.
         */
-       dma_mask_ptr = (u64 *)of_device_get_match_data(&pdev->dev);
-       if (!dma_mask_ptr)
-               dma_mask_ptr = &dma_mask_32;
+       if (of_device_get_match_data(&pdev->dev))
+               dma_mask_64 = true;
 
-       ret = dma_coerce_mask_and_coherent(&pdev->dev, *dma_mask_ptr);
+       ret = dma_coerce_mask_and_coherent(&pdev->dev,
+               dma_mask_64 ? DMA_BIT_MASK(64) : DMA_BIT_MASK(32));
        if (ret)
                return ret;
 
@@ -200,7 +197,7 @@ static void uhci_hcd_platform_shutdown(struct platform_device *op)
 static const struct of_device_id platform_uhci_ids[] = {
        { .compatible = "generic-uhci", },
        { .compatible = "platform-uhci", },
-       { .compatible = "aspeed,ast2700-uhci", .data = &dma_mask_64},
+       { .compatible = "aspeed,ast2700-uhci", .data = (void *)1 },
        {}
 };
 MODULE_DEVICE_TABLE(of, platform_uhci_ids);