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Date:   Thu, 18 Aug 2022 16:26:37 -0400
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Subject: Re: [External] Re: [PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when
 it's supported
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To:     Lyude Paul <lyude@redhat.com>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>
CC:     Jani Nikula <jani.nikula@linux.intel.com>,
        <joonas.lahtinen@linux.intel.com>, <rodrigo.vivi@intel.com>,
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        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        "Hans de Goede" <hdegoede@redhat.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        <intel-gfx@lists.freedesktop.org>,
        <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>
References: <20220816025217.618181-1-kai.heng.feng@canonical.com>
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From:   Mark Pearson <markpearson@lenovo.com>
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On 2022-08-17 13:56, Lyude Paul wrote:
> Adding Mark Pearson from Lenovo to this, Mark for reference the original patch
> is here:
> 
> https://patchwork.freedesktop.org/patch/497807/?series=107312&rev=1>> 
> Comments from me down below
> 
> On Wed, 2022-08-17 at 09:02 +0800, Kai-Heng Feng wrote:
>> On Wed, Aug 17, 2022 at 2:24 AM Lyude Paul <lyude@redhat.com> wrote:
>>>
>>> On Tue, 2022-08-16 at 19:29 +0800, Kai-Heng Feng wrote:
>>>> On Tue, Aug 16, 2022 at 4:06 PM Jani Nikula <jani.nikula@linux.intel.com> wrote:
>>>>>
>>>>> On Tue, 16 Aug 2022, Kai-Heng Feng <kai.heng.feng@canonical.com> wrote:
>>>>>> On mobile workstations like HP ZBook Fury G8, iGFX's DP-IN can switch to
>>>>>> dGFX so external monitors are routed to dGFX, and more monitors can be
>>>>>> supported as result.
>>>>>>
>>>>>> To switch the DP-IN to dGFX, the driver needs to invoke _DSM function 20
>>>>>> on intel_dsm_guid2. This method is described in Intel document 632107.
>>>
>>> Is this documentation released anywhere? We've been wondering about these
>>> interfaces for quite a long time, and it would be good to know if there's docs
>>> for this we haven't really been seeing.
>>>
>>>>>
>>>>> Is this the policy decision that we want to unconditionally make,
>>>>> though?
>>>>
>>>> I believes so, so more external monitors can be supported at the same time.
>>>>
>>>> Kai-Heng
>>>
>>> Is this for systems with dual Intel GPUs? I ask because if this affects
>>> Intel/Nvidia hybrid systems then this is a huge no from me. Nouveau is able to
>>> support these systems, but at a limited capacity. This would imply that we are
>>> making external displays work for users of the nvidia proprietary driver, at
>>> the expense making external display support for mainline kernel users
>>> substantially worse for people who are using the mainline kernel. Which isn't
>>> a choice we should be making, because nvidia's OOT driver is not a mainline
>>> kernel driver.
>>
>> Yes it's for Intel/NVIDIA hybrid systems.
>>
>> The problem is that hardware vendor design the systems to use NVIDIA
>> for external displays, so using external displays on Intel are never
>> tested by the vendors.
>> I don't think that's any good either.
>>
> 
> Sigh, the constant forcing of nvidia hardware into laptops from vendors is
> seriously something I wish they would knock it off with considering they're
> basically the most difficult hardware vendor to work with.
> 
> Anyway, if we -need- to route displays through the external GPU then we can.
> But I'd like to at least get convinced first that this is an actual necessity
> we should expect for multiple vendors, or the exception to the rule. Because
> if these laptops are capable of driving displays through Intel, at the moment
> not doing that is a huge downgrade in terms of functionality. -Especially- if
> these machines were already working in the field as-is. Probably worth noting
> I don't think I have yet to actually hear of any complaints about this being
> the case, and I'd like to also make sure this isn't a change being done for
> one or two vendors when most vendors aren't actually doing something like
> this.
> 
> Note that for a lot of systems it won't -technically- be a big difference
> since the current situation in the market right now is that a lot of laptops
> will have all their external displays routed through the nvidia GPU and
> nowhere else. It's not great compared to just being able to use the well
> supported Intel GPU for everything though. And if we're controlling display
> routing through ACPI, that implies things aren't directly hooked up and
> someone went through the hassle of adding a display mux - which kind of seems
> like a waste of engineering effort and money if it can't actually be used for
> muxing between the two GPUs. Especially considering that up until very
> recently muxes had more or less been dropped from the majority of laptop
> vendors (I think Dell was an exception for this fwiw).
> 
> Mark, since you're from Lenovo can you help to confirm this as well?

I'll have to do some checking for this years models and get back to you
I know on last years that we had a HW mux available on the P1. There
wasn't one on the P17 (and I'm not sure about the P15).

My understanding is the Intel display just wasn't available at all
for external display on the P17 (and I do agree with your comments on
the wiseness of this!). I believe it was hardwired with no way to switch
it - we lost a sale from this, and if there had been an alternative we
would have pursued it.
I'll confirm with the HW/FW team.

We also have lots of users on Legion gaming systems - but unfortunately I
don't know what happens on those platforms as they're not in our Linux
program.

Mark