linux-kernel - Re: [PATCH V12 3/7] dma: add Qualcomm Technologies HIDMA management driver

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Date:	Fri, 15 Jan 2016 18:08:51 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Sinan Kaya <okaya@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>
CC:	dmaengine@...r.kernel.org, timur@...eaurora.org,
	devicetree@...r.kernel.org, cov@...eaurora.org,
	vinod.koul@...el.com, jcm@...hat.com, agross@...eaurora.org,
	arnd@...db.de, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org,
	Vikram Sethi <vikrams@...eaurora.org>, shankerd@...eaurora.org
Subject: Re: [PATCH V12 3/7] dma: add Qualcomm Technologies HIDMA management
 driver

On 15/01/16 17:44, Sinan Kaya wrote:
>>>

[...]

>> You may want to drop the "hypervisor" designation, BTW, because this has
>> no real connection to virtualisation.
>>
> 
> Would you use host/guest relationship?

Not even that. This is a host/user relationship, as VFIO is in no way
virtualisation specific. It just gives you a way to make a device
accessible to userspace. KVM is just a specialised instance of a more
generic problem.

> 
>>>
>>> Once the guest machine is shutdown, VFIO driver still owns the channel device. It can
>>> assign the device to another guest machine.
>>>
>>>> - Does the HYP side requires any context switch (and how is that done)?
>>> No communication is needed.
>>>
>>>> - What makes it safe?
>>> No communication is needed.
>>>
>>>>
>>>> Without any of this information (and pointer to the code to back it up),
>>>> I'm very reluctant to take any of this.
>>>
>>> Please let me know what exactly is not clear. 
>>>
>>> You don't write a virtualization driver for 8139too driver. The driver works whether it is running in the 
>>> guest machine or the hypervisor. 
>>
>> Exactly. No hypervisor code needed whatsoever. So please get rid of this
>> hypervisor nonsense! ;-)
>>
> 
> I need the management driver for administrative purposes and common initialization. 
> I like the split SW design as it follows the HW design too.

I have no problem with the split design (whatever floats your boat),
more with the terminology which I find very confusing. It would be a lot
better if you stuck with management (host) and client (user), or some
other general terminology.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...