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

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Date:   Sat, 5 May 2018 15:33:11 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jia-Ju Bai <baijiaju1990@...il.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 Friday 04 May 2018 09:59 PM, Lorenzo Pieralisi wrote:
> 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.

sorry, missed this before.

Acked-by: Kishon Vijay Abraham I <kishon@...com>
> 
> 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
>>