linux-kernel - Re: About TRB_TO_EP

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Message-ID: <20130806090654.GA27268@kroah.com>
Date:	Tue, 6 Aug 2013 17:06:54 +0800
From:	"'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>
To:	"Du, ChangbinX" <changbinx.du@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"balbi@...com" <balbi@...com>,
	"sarah.a.sharp@...uxfoundation.org" 
	<sarah.a.sharp@...uxfoundation.org>, "Wu, Hao" <hao.wu@...el.com>,
	"Tang, Jianqiang" <jianqiang.tang@...el.com>,
	"Zhuang, Jin Can" <jin.can.zhuang@...el.com>,
	"Huang, Xiaochao" <xiaochao.huang@...el.com>
Subject: Re: About TRB_TO_EP_INDEX() macro using

On Tue, Aug 06, 2013 at 08:59:32AM +0000, Du, ChangbinX wrote:
> > On Mon, Aug 05, 2013 at 08:07:25AM +0000, Du, ChangbinX wrote:
> > > Recently when I check xHCI code, find that some functions try to get EP index
> > > from a Command Completion Event TRB via TRB_TO_EP_INDEX() macro.
> > >
> > > This is totally wrong. The macro definition is:
> > >
> > > 	#define TRB_TO_EP_INDEX(p)		((((p) & (0x1f << 16)) >> 16) - 1)
> > >
> > > TRB_TO_EP_INDEX only applies to Transfer Event TRB. But for Command
> > > Completion Event TRB, there is no Endpoint ID field. So, we cannot directly
> > > get EP index from these TRBs, but we can find it by the TRB Pointer.
> > >
> > > Here list two functions for you to check:
> > > 	handle_stopped_endpoint()
> > > 	handle_reset_ep_completion()
> > 
> > Care to send a patch showing how you would change this if it is
> > incorrect?
> > 
> > thanks,
> > 
> > greg k-h
> > --
> 
> Hello, Greg k-h. I am not very sure about this issue. If this is true, kernel will panic when 
> invoking above functions. I want someone help to confirm if I miss something. If it's really 
> a bug, I will work out a patch to fix it.

That's not how kernel development works, sorry.  If you think this is an
issue, try to reproduce it and then create a patch.

thanks,

greg k-h
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