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Date:   Tue, 29 Jun 2021 14:18:06 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Bing Fan <hptsfb@gmail.com>
Cc:     linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm pl011 serial: support multi-irq request
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References: <1624930164-18411-1-git-send-email-hptsfb@gmail.com>
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 <d2ba9f70-2ace-d796-8ce8-fd56d73d145b@gmail.com>
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On Tue, Jun 29, 2021 at 07:32:36PM +0800, Bing Fan wrote:
> hello,
> 
> replied as below.
> 
> and new patch is at the bottom.

Please submit this properly as the documentation says to do so, I can't
take an attachment :(

> > > +	struct amba_device *amba_dev = (struct amba_device *)uap->port.dev;
> > Are you sure you can just cast this like this?  Did you test this?
> 
> 
> Yes, i have tested and applied in my project.
> 
> The function pl011_probe calls pl011_setup_port with &amba_dev->dev and uap
> params;
> 
> and pl011_setup_port set uap->port.dev to the address of amba_dev->dev;
> 
> the two structs' relationship is:
> 
>     struct amba_device {
> 
>         struct device dev;
> 
>         ……
> 
>     };
> 
> When pointer(uap->port.dev) points to amba_dev->dev address, the momery
> actully stores
> 
> content of struct amba_device; so the cast assignment can be forced to
> amba_dev.

That is now how this should work, use the correct container_of() cast
instead.  That will always work no matter where struct device is in the
structure.  You got lucky here :)

> > > +
> > > +	if (!amba_dev)
> > > +		return -1;
> > Do not make up error numbers, return a specific -ERR* value.
> 
> changed to "return -ENODEV"

So this changed the logic of this function, is that ok?

> > 
> > And how can this happen?
> 
> The function pl011_setup_port isn't called, event pl011_probe isn't called.

And how can that ever happen?


thanks,

greg k-h