linux-kernel - Re: [PATCH v3 4/5] arm64: dts: qcom: x1e80100-crd: add rtc offset to set rtc time

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Message-ID: <ZxIt_oct24WuIssO@hovoldconsulting.com>
Date: Fri, 18 Oct 2024 11:44:30 +0200
From: Johan Hovold <johan@...nel.org>
To: Jonathan Marek <jonathan@...ek.ca>
Cc: linux-arm-msm@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" <devicetree@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 4/5] arm64: dts: qcom: x1e80100-crd: add rtc offset to
 set rtc time

On Wed, Oct 16, 2024 at 09:31:00AM -0400, Jonathan Marek wrote:
> On 10/16/24 2:51 AM, Johan Hovold wrote:
> > On Mon, Oct 14, 2024 at 08:47:29PM -0400, Jonathan Marek wrote:

> >> Note: the 0xbc offset is arbitrary, it just needs to not be already in use.
> > 
> > How did you verify that nothing is using this offset on this platform? I
> > assume we need someone with access to the docs to make sure it's not in
> > use as we did for sc8280xp.
>
> AFAIK qcom allocate things from the start of the SDAM, so allocating 
> from the end of the SDAM should be safe. And AFAIK this is supposed to 
> be a general purpose HLOS (linux/windows) SDAM block, so should be 
> mostly free to use.

>From what I understand these registers are also used for things like
programmable LEDs (e.g. see 24e2d05d1b68 ("leds: Add driver for Qualcomm
LPG")). And who knows what else.

It would be good if someone from Qualcomm could confirm that these bytes
are free for use before merging. I've started asking around.

Johan