linux-kernel - Re: [PATCH] USB: host: ehci: Add error handlinginehci_mxc_drv

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Date:   Sat, 9 May 2020 09:13:22 +0800
From:   Tang Bin <tangbin@...s.chinamobile.com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, stern@...land.harvard.edu,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: host: ehci: Add error handlinginehci_mxc_drv_probe()

Hi Sergei:

On 2020/5/9 4:27, Sergei Shtylyov wrote:
> On 05/08/2020 06:03 PM, Tang Bin wrote:
>
>>>>> On Fri, May 08, 2020 at 07:44:53PM +0800, Tang Bin wrote:
>>>>>> The function ehci_mxc_drv_probe() does not perform sufficient error
>>>>>> checking after executing platform_get_irq(), thus fix it.
>>>>>>
>>>>>> Fixes: 7e8d5cd93fa ("USB: Add EHCI support for MX27 and MX31 based boards")
>>>>>> Signed-off-by: Zhang Shengju <zhangshengju@...s.chinamobile.com>
>>>>>> Signed-off-by: Tang Bin <tangbin@...s.chinamobile.com>
>>>>>> ---
>>>>>>     drivers/usb/host/ehci-mxc.c | 2 ++
>>>>>>     1 file changed, 2 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/usb/host/ehci-mxc.c b/drivers/usb/host/ehci-mxc.c
>>>>>> index a1eb5ee77..a0b42ba59 100644
>>>>>> --- a/drivers/usb/host/ehci-mxc.c
>>>>>> +++ b/drivers/usb/host/ehci-mxc.c
>>>>>> @@ -50,6 +50,8 @@ static int ehci_mxc_drv_probe(struct platform_device *pdev)
>>>>>>         }
>>>>>>         irq = platform_get_irq(pdev, 0);
>>>>>> +    if (irq < 0)
>>>>>> +        return irq;
>>>>> <= ?
>>>> In the file 'drivers/base/platform.c'， the function platform_get_irq() is
>>>> explained and used as follows:
>>>>
>>>>        * Gets an IRQ for a platform device and prints an error message if
>>>> finding the
>>>>        * IRQ fails. Device drivers should check the return value for errors so
>>>> as to
>>>>        * not pass a negative integer value to the request_irq() APIs.
>>>>        *
>>>>        * Example:
>>>>        *        int irq = platform_get_irq(pdev, 0);
>>>>        *        if (irq < 0)
>>>>        *            return irq;
>>>>        *
>>>>        * Return: IRQ number on success, negative error number on failure.
>>>>
>>>> And in my hardware experiment, even if I set the irq failed deliberately in
>>>> the DTS, the returned value is negative instead of zero.
>>> Please read the thread at
>>>      https://lore.kernel.org/r/20200501224042.141366-1-helgaas%40kernel.org
>>> for more details about this.
>>>
>> Great, It looks beautiful, finally someone took a knife to the file 'platform.c'.
>     I thought I did that already couple years ago, when returned 0 from platform_get_irq() could mean both IRQ # and error... :-)
Can you tell me what platform can returned 0? I want to do this test in 
the hardware.
>> I have been studied this place for a long time, and don't know what platform can return 0, which made me curious.
>>
>> So the example should be:
>>
>>       *        int irq = platform_get_irq(pdev, 0);
>>       *        if (irq <= 0)
>>       *            return irq;
>     And you then return 0 (success) as if your probe() succeeded. Congratulations! :-P

Thanks,

Tang Bin