linux-kernel - Re: [PATCH v1 1/9] drivers: hv: dxgkrnl: Driver initialization and creation of dxgadapter

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Date:   Thu, 13 Jan 2022 16:08:07 -0800
From:   Iouri Tarassov <iourit@...ux.microsoft.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, linux-hyperv@...r.kernel.org,
        linux-kernel@...r.kernel.org, spronovo@...rosoft.com
Subject: Re: [PATCH v1 1/9] drivers: hv: dxgkrnl: Driver initialization and
 creation of dxgadapter

On 1/12/2022 11:46 PM, Greg KH wrote:
> On Wed, Jan 12, 2022 at 11:55:06AM -0800, Iouri Tarassov wrote:
> > +	dev_dbg(dxgglobaldev, "%s: %x:%x %p %pUb\n",
> > +		    __func__, adapter->luid.b, adapter->luid.a, hdev->channel,
> > +		    &hdev->channel->offermsg.offer.if_instance);
>
> When I see something like "global device pointer", that is a HUGE red
> flag.
>
> No driver should ever have anything that is static to the driver like
> this, it should always be per-device.  Please use the correct device
> model here, which does not include a global pointer, but rather unique
> ones that are given to you by the driver core.  That way you are never
> tied to only "one device per system" as that is a constraint that you
> will have to fix eventually, might as well do it all correctly the first
> time as it is not any extra effort to do so
Hi Greg,

dxgglobaldev is a pointer to the global driver data. By design there is a
single hyper-v VM bus and a single corresponding /dev/dxg device.
Virtual GPU adapters are present on the VM bus. /dev/dxg device is used
to enumerate all virtual GPUs, which are accessible only via IOCTLs
to /dev/dxg. dxgglobaldev has a list of all vGPU adapters and
other global driver state. This follows the design on Windows where a single
global object in dxgkrnl.sys driver is used to enumerate and access all
GPU devices. This is also how the public D3DKMT interface to dxgkrnl is
structured.

Thanks
Iouri