Re: [PATCH 1/1] Staging: hv: Move the mouse driver out of staging

[Dmitry Torokhov]

Hi K. Y,

On Mon, Nov 07, 2011 at 01:04:53AM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Dmitry Torokhov [mailto:dmitry.torokhov@xxxxxxxxx]
> > Sent: Saturday, November 05, 2011 2:48 AM
> > To: KY Srinivasan
> > Cc: gregkh@xxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > devel@xxxxxxxxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxx; ohering@xxxxxxxx;
> > joe@xxxxxxxxxxx; jkosina@xxxxxxx
> > Subject: Re: [PATCH 1/1] Staging: hv: Move the mouse driver out of staging
> > 
> > Hi KY,
> 
> Dimitry,
> 
> Let me begin by thanking you for taking the time to review. I have incorporated
> pretty much all your suggestions.

Thank you very much for considering my suggestions.

> > 
> > Instead of potentially ever-increasing buffer that you also allocate
> > (and it looks like leaking on every callback invocation) can you just
> > repeat the read if you know that there are more data and use single
> > pre-allocated buffer?
> 
> The ring-buffer protocol is such that we need to consume the full message.
> Also, why do you say we are leaking memory?

Ah, OK, I see, we keep reading until read returns 0-sized reply and then
we free the buffer... Never mind then.

> > > +
> > > +	hid_dev->ll_driver = &mousevsc_ll_driver;
> > > +	hid_dev->driver = &mousevsc_hid_driver;
> > 
> > You are not really hid driver; you are more of a "provider" so why do
> > you need to set hid_dev->driver in addition to hid_dev->ll_driver?
> > 
> True, but hid_parse_report() expects that the driver field be set; so I
> need to fake this.

If you supply .parse() method for your mousevsc_ll_driver structure and
call hid_parse_report() from it then HID core will set the default
driver and call parse at appropriate time.

>  
> > > +	hid_dev->bus = BUS_VIRTUAL;
> > > +	hid_dev->vendor = input_dev->hid_dev_info.vendor;
> > > +	hid_dev->product = input_dev->hid_dev_info.product;
> > > +	hid_dev->version = input_dev->hid_dev_info.version;
> > > +	input_dev->hid_device = hid_dev;
> > > +
> > > +	sprintf(hid_dev->name, "%s", "Microsoft Vmbus HID-compliant Mouse");
> > 
> > strlcpy?
> > 
> > > +
> > > +	ret = hid_parse_report(hid_dev, input_dev->report_desc,
> > > +				input_dev->report_desc_size);
> > > +
> > > +	if (ret) {
> > > +		hid_err(hid_dev, "parse failed\n");
> > > +		goto probe_err1;
> > > +	}
> > > +
> > > +	ret = hid_hw_start(hid_dev, HID_CONNECT_HIDINPUT |
> > HID_CONNECT_HIDDEV);
> > 
> > Why do you need to call hid_hw_start instead of letting HID core figure
> > it out for you?
> 
> I am not a hid expert; but all  hid low level drivers appear to do this.
> Initially, I was directly invoking hid_connect() directly and based on your
> Input, I chose to use hid_hw_start() which all other drivers are using.

Note that the users of hid_hw_start() actually are not low level
drivers, such as usbhid or bluetooth hidp, but higher-level drivers,
such as hid-wacom, hid-a4tech, etc. Since your driver is a low-level
driver (a provider so to speak) it should not call hid_hw_start() on its
own but rather wait for the hid code to do it.

Still, I am not a HID expert either so I'll defer to Jiri here.

Thanks.

-- 
Dmitry
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