linux-kernel - Re: [PATCH 2/2] uacce: add uacce module

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Date:   Tue, 20 Aug 2019 07:33:41 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     zhangfei <zhangfei.gao@...aro.org>
Cc:     "zhangfei.gao@...mail.com" <zhangfei.gao@...mail.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-accelerators@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Kenneth Lee <liguozhu@...ilicon.com>,
        Zaibo Xu <xuzaibo@...wei.com>,
        Zhou Wang <wangzhou1@...ilicon.com>
Subject: Re: [PATCH 2/2] uacce: add uacce module

On Tue, Aug 20, 2019 at 08:36:50PM +0800, zhangfei wrote:
> Hi, Greg
> 
> On 2019/8/19 下午6:24, Greg Kroah-Hartman wrote:
> > > > > +static int uacce_create_chrdev(struct uacce *uacce)
> > > > > +{
> > > > > +	int ret;
> > > > > +
> > > > > +	ret = idr_alloc(&uacce_idr, uacce, 0, 0, GFP_KERNEL);
> > > > > +	if (ret < 0)
> > > > > +		return ret;
> > > > > +
> > > > Shouldn't this function create the memory needed for this structure?
> > > > You are relying ont he caller to do it for you, why?
> > > I think you mean uacce structure here.
> > > Yes, currently we count on caller to prepare uacce structure and call
> > > uacce_register(uacce).
> > > We still think this method is simpler, prepare uacce, register uacce.
> > > And there are other system using the same method, like crypto
> > > (crypto_register_acomp), nand, etc.
> > crypto is not a subsystem to ever try to emulate :)
> > 
> > You are creating a structure with a lifetime that you control, don't
> > have someone else create your memory, that's almost never what you want
> > to do.  Most all driver subsystems create their own memory chunks for
> > what they need to do, it's a much better pattern.
> > 
> > Especially when you get into pointer lifetime issues...
> OK, understand now, thanks for your patience.
> will use this instead.
> struct uacce_interface {
>         char name[32];
>         unsigned int flags;
>         struct uacce_ops *ops;
> };
> struct uacce *uacce_register(struct device *dev, struct uacce_interface
> *interface);

What?  Why do you need a structure?  A pointer to the name and the ops
should be all that is needed, right?

And 'dev' here is a pointer to the parent, right?  Might want to make
that explicit in the name of the variable :)

> > > > > +
> > > > > +static int uacce_dev_match(struct device *dev, void *data)
> > > > > +{
> > > > > +	if (dev->parent == data)
> > > > > +		return -EBUSY;
> > > > There should be in-kernel functions for this now, no need for you to
> > > > roll your own.
> > > Sorry, do not find this function.
> > > Only find class_find_device, which still require match.
> > It is in linux-next, look there...
> > 
> Suppose you mean the funcs: device_match_name,
> device_match_of_node,device_match_devt etc.
> Here we need dev->parent, there still no such func.

You should NEVER be matching on a parent.  If so, your use of the driver
model is wrong :)

Remind me to really review the use of the driver core code in your next
submission of this series please, I think it needs it.

thanks,

greg k-h