linux-kernel - Re: [PATCH v2] usb: dwc2: hcd_queue: Fix use of floating point literal

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Message-ID: <YYVKj/+4snhK6/vs@donbot>
Date:   Fri, 5 Nov 2021 15:15:27 +0000
From:   John Keeping <john@...anate.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Minas Harutyunyan <hminas@...opsys.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] usb: dwc2: hcd_queue: Fix use of floating point
 literal

On Fri, Nov 05, 2021 at 07:58:03AM -0700, Nathan Chancellor wrote:
> A new commit in LLVM causes an error on the use of 'long double' when
> '-mno-x87' is used, which the kernel does through an alias,
> '-mno-80387' (see the LLVM commit below for more details around why it
> does this).
> 
>  drivers/usb/dwc2/hcd_queue.c:1744:25: error: expression requires  'long double' type support, but target 'x86_64-unknown-linux-gnu' does not support it
>                          delay = ktime_set(0, DWC2_RETRY_WAIT_DELAY);
>                                              ^
>  drivers/usb/dwc2/hcd_queue.c:62:34: note: expanded from macro 'DWC2_RETRY_WAIT_DELAY'
>  #define DWC2_RETRY_WAIT_DELAY (1 * 1E6L)
>                                  ^
>  1 error generated.
> 
> This happens due to the use of a 'long double' literal. The 'E6' part of
> '1E6L' causes the literal to be a 'double' then the 'L' suffix promotes
> it to 'long double'.
> 
> There is no visible reason for a floating point value in this driver, as
> the value is only used as a parameter to a function that expects an
> integer type. Use NSEC_PER_MSEC, which is the same integer value as
> '1E6L', to avoid changing functionality but fix the error.
> 
> Fixes: 6ed30a7d8ec2 ("usb: dwc2: host: use hrtimer for NAK retries")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1497
> Link: https://github.com/llvm/llvm-project/commit/a8083d42b1c346e21623a1d36d1f0cadd7801d83
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Reviewed-by: John Keeping <john@...anate.com>

> ---
> 
> v1 -> v2: https://lore.kernel.org/r/20211104215923.719785-1-nathan@kernel.org/
> 
> * Use NSEC_PER_MSEC instead of USEC_PER_SEC, as the units of the second
>   parameter of ktime_set is nanoseconds. Thanks to John Keeping for
>   pointing this out.
> 
> * Pick up Nick's review tag.
> 
>  drivers/usb/dwc2/hcd_queue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc2/hcd_queue.c b/drivers/usb/dwc2/hcd_queue.c
> index 89a788326c56..24beff610cf2 100644
> --- a/drivers/usb/dwc2/hcd_queue.c
> +++ b/drivers/usb/dwc2/hcd_queue.c
> @@ -59,7 +59,7 @@
>  #define DWC2_UNRESERVE_DELAY (msecs_to_jiffies(5))
>  
>  /* If we get a NAK, wait this long before retrying */
> -#define DWC2_RETRY_WAIT_DELAY (1 * 1E6L)
> +#define DWC2_RETRY_WAIT_DELAY (1 * NSEC_PER_MSEC)
>  
>  /**
>   * dwc2_periodic_channel_available() - Checks that a channel is available for a
> 
> base-commit: d4439a1189f93d0ac1eaf0197db8e6b3e197d5c7
> -- 
> 2.34.0.rc0
>