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Date:   Fri, 5 Nov 2021 13:08:48 +0000
From:   John Keeping <john@metanate.com>
To:     Nathan Chancellor <nathan@kernel.org>
Cc:     Minas Harutyunyan <hminas@synopsys.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev
Subject: Re: [PATCH] usb: dwc2: hcd_queue: Fix use of floating point literal
Message-ID: <YYUs4PME9QizsPTt@donbot>
References: <20211104215923.719785-1-nathan@kernel.org>
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On Thu, Nov 04, 2021 at 02:59:23PM -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 USEC_PER_SEC, 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@kernel.org>
> ---
>  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..bdf1927e1be1 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 * USEC_PER_SEC)

Using USEC_PER_SEC here seems quite weird.  This is used as:

	delay = ktime_set(0, DWC2_RETRY_WAIT_DELAY);

so the units are nanoseconds.

Maybe NSEC_PER_MSEC would better indicate the intent here?