Re: [PATCH v3] efifb: avoid reconfiguration of BAR that covers the framebuffer

From: Sinan Kaya <okaya@codeaurora.org>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>
Cc: "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	linux-pci <linux-pci@vger.kernel.org>,
	Peter Jones <pjones@redhat.com>, Heyi Guo <heyi.guo@linaro.org>,
	Lukas Wunner <lukas@wunner.de>,
	Hanjun Guo <hanjun.guo@linaro.org>,
	Yinghai Lu <yinghai@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v3] efifb: avoid reconfiguration of BAR that covers the framebuffer
Date: Thu, 30 Mar 2017 09:50:04 -0400	[thread overview]
Message-ID: <ae87ae28-f50d-095f-576e-f3fd7f96dea2@codeaurora.org> (raw)
In-Reply-To: <CAKv+Gu8YjySTDMgsrtGqEPMOtVhHc8gvTHZ4C5Ga8OTYdC9R3A@mail.gmail.com>

On 3/30/2017 9:38 AM, Ard Biesheuvel wrote:
> On 30 March 2017 at 11:09, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> On 30 March 2017 at 11:05, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com> wrote:
>>> On Thu, Mar 30, 2017 at 09:46:39AM +0100, Ard Biesheuvel wrote:
>>>
>>> [...]
>>>
>>>>> I'm asking why we don't fix the actual problem in PCIe ARM64 adaptation instead
>>>>> of working around it by quirks.
>>>>>
>>>>> I don't see any reason why ACPI ARM64 should carry the burden of legacy systems.
>>>>>
>>>>> Legacy only applies to DT based systems.
>>>>>
>>>>
>>>> I fully agree with this point: ACPI implies firmware, and so we should
>>>> be able to rely on firmware to have initialized the PCIe subsystem by
>>>> the time the kernel gets to access it.
>>>
>>> https://lkml.org/lkml/2016/3/3/458
>>>
>>
>> I don't think the fact that at least one system existed over a year
>> ago whose UEFI assigned resources incorrectly should prevent us from
>> being normative in this case.
> 
> In any case, given that EFIFB is enabled by default on some distros,
> and the fact that DT boot is affected as well, I should get this patch
> in to prevent serious potential issues that could arise when someone
> with a graphical UEFI stack updates to such a new kernel.
> 
> So I think we are in agreement that this is needed on both ARM and
> arm64, since their PCI configuration is usually not preserved. The
> open question is whether there is any harm in enabling it for x86 as
> well.
> 

Agreed, the other issue is about compatibility with UEFI and future
proofing Linux for other potential issues like hotplug reservation.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

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