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From:   "Quan, Evan" <Evan.Quan@amd.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     "rafael@kernel.org" <rafael@kernel.org>,
        "lenb@kernel.org" <lenb@kernel.org>,
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        "Limonciello, Mario" <Mario.Limonciello@amd.com>,
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        "Lazar, Lijo" <Lijo.Lazar@amd.com>,
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Subject: RE: [PATCH V5 1/9] drivers core: Add support for Wifi band RF
 mitigations
Thread-Topic: [PATCH V5 1/9] drivers core: Add support for Wifi band RF
 mitigations
Thread-Index: AQHZqz5nCvlP5HKi7kqHZhT1UyZB3K+kDOyAgATrEhCAAKJtgIACaF9A
Date:   Thu, 6 Jul 2023 02:58:53 +0000
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References: <20230630103240.1557100-1-evan.quan@amd.com>
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[AMD Official Use Only - General]

Hi Andrew,

I discussed with Mario about your proposal/concerns here.
We believe some changes below might address your concerns.
- place/move the wbrf_supported_producer check inside acpi_amd_wbrf_add_exc=
lusion and acpi_amd_wbrf_add_exclusion
- place the wbrf_supported_consumer check inside acpi_amd_wbrf_retrieve_exc=
lusions
So that the wbrf_supported_producer and wbrf_supported_consumer can be drop=
ped.
We made some prototypes and even performed some tests which showed technica=
lly it is absolutely practicable.

However, we found several issues with that.
- The overhead caused by the extra _producer/_consumer check on every calli=
ng of wbrf_add/remove/retrieve_ecxclusion.
  Especially when you consider there might be multiple producers and consum=
ers in the system at the same time. And some of
  them might do in-use band/frequency switching frequently.
- Some extra costs caused by the "know it only at the last minute". For exa=
mple, to support WBRF, amdgpu driver needs some preparations: install the n=
otification hander,
  setup the delay workqueue(to handle possible events flooding) and even no=
tify firmware engine to be ready. However, only on the 1st notification rec=
eiving,
  it is realized(reported by wbrf_supported_consumer check) the WBRF featur=
e is actually not supported. All those extra costs can be actually avoided =
if we can know the WBRF is not supported at first.
  This could happen to other consumers and producers too.

After a careful consideration, we think the changes do not benefit us much.=
 It does not deserve us to spend extra efforts.
Thus we would like to stick with original implementations. That is to have =
wbrf_supported_producer and wbrf_supported_consumer interfaces exposed.
Then other drivers/subsystems can do necessary wbrf support check in advanc=
e and coordinate their actions accordingly.
Please let us know your thoughts.

BR,
Evan
> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Tuesday, July 4, 2023 9:07 PM
> To: Quan, Evan <Evan.Quan@amd.com>
> Cc: rafael@kernel.org; lenb@kernel.org; Deucher, Alexander
> <Alexander.Deucher@amd.com>; Koenig, Christian
> <Christian.Koenig@amd.com>; Pan, Xinhui <Xinhui.Pan@amd.com>;
> airlied@gmail.com; daniel@ffwll.ch; johannes@sipsolutions.net;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com; Limonciello, Mario <Mario.Limonciello@amd.com>;
> mdaenzer@redhat.com; maarten.lankhorst@linux.intel.com;
> tzimmermann@suse.de; hdegoede@redhat.com; jingyuwang_vip@163.com;
> Lazar, Lijo <Lijo.Lazar@amd.com>; jim.cromie@gmail.com;
> bellosilicio@gmail.com; andrealmeid@igalia.com; trix@redhat.com;
> jsg@jsg.id.au; arnd@arndb.de; linux-kernel@vger.kernel.org; linux-
> acpi@vger.kernel.org; amd-gfx@lists.freedesktop.org; dri-
> devel@lists.freedesktop.org; linux-wireless@vger.kernel.org;
> netdev@vger.kernel.org
> Subject: Re: [PATCH V5 1/9] drivers core: Add support for Wifi band RF
> mitigations
>
> > > What is the purpose of this stage? Why would it not be supported for
> > > this device?
> > This is needed for wbrf support via ACPI mechanism. If BIOS(AML code)
> > does not support the wbrf adding/removing for some device, it should
> speak that out so that the device can be aware of that.
>
> How much overhead is this adding? How deep do you need to go to find the
> BIOS does not support it? And how often is this called?
>
> Where do we want to add complexity? In the generic API? Or maybe a little
> deeper in the ACPI specific code?
>
>        Andrew