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

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Date:   Fri, 8 May 2020 23:27:38 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     Tang Bin <tangbin@...s.chinamobile.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     stern@...land.harvard.edu, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Zhang Shengju <zhangshengju@...s.chinamobile.com>
Subject: Re: [PATCH] USB: host: ehci: Add error handlinginehci_mxc_drv_probe()

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... :-)

> 
> 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

MBR, Sergei