linux-kernel - Re: [PATCH] pci: endpoint: Replace mdelay with usleep_range in pci_epf_test

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Message-ID: <20180504162932.GA16953@e107981-ln.cambridge.arm.com>
Date:   Fri, 4 May 2018 17:29:32 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, kishon@...com
Cc:     bhelgaas@...gle.com, nsekhar@...com, john@...anate.com,
        shawn.lin@...k-chips.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci: endpoint: Replace mdelay with usleep_range in
 pci_epf_test_write

On Tue, Apr 10, 2018 at 09:04:06PM +0800, Jia-Ju Bai wrote:
> pci_epf_test_write() is never called in atomic context.
> 
> The call chain ending up at pci_epf_test_write() is:
> [1] pci_epf_test_write() <- pci_epf_test_cmd_handler()
> 
> pci_epf_test_cmd_handler() is set as a parameter of INIT_DELAYED_WORK() 
> in pci_epf_test_probe().
> This function is not called in atomic context.
> 
> Despite never getting called from atomic context, pci_epf_test_write()
> calls mdelay() to busily wait.
> This is not necessary and can be replaced with usleep_range() to
> avoid busy waiting.
> 
> This is found by a static analysis tool named DCNS written by myself.
> And I also manually check it.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  drivers/pci/endpoint/functions/pci-epf-test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

I'd request Kishon's ACK on this.

Thanks,
Lorenzo

> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index f9308c2..2f0642e 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -237,7 +237,7 @@ static int pci_epf_test_write(struct pci_epf_test *epf_test)
>  	 * wait 1ms inorder for the write to complete. Without this delay L3
>  	 * error in observed in the host system.
>  	 */
> -	mdelay(1);
> +	usleep_range(1000, 2000);
>  
>  	kfree(buf);
>  
> -- 
> 1.9.1
>