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Date:   Thu, 14 Sep 2023 16:09:22 +0200
From:   Stephan Gerhold <stephan@gerhold.net>
To:     Konrad Dybcio <konrad.dybcio@linaro.org>
Cc:     Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Andy Gross <agross@kernel.org>, linux-arm-msm@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/9] arm64: dts: qcom: msm8916: Reserve firmware memory
 dynamically
Message-ID: <ZQMUDia6cYA0mGmL@gerhold.net>
References: <20230911-msm8916-rmem-v1-0-b7089ec3e3a1@gerhold.net>
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 <9b1beb38-9ec2-4bdb-97f5-fccf98d3b0c3@linaro.org>
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On Wed, Sep 13, 2023 at 09:39:50PM +0200, Konrad Dybcio wrote:
> On 13.09.2023 12:14, Stephan Gerhold wrote:
> > On Wed, Sep 13, 2023 at 10:12:12AM +0100, Bryan O'Donoghue wrote:
> >> On 13/09/2023 10:06, Konrad Dybcio wrote:
> >>> On 11.09.2023 19:41, Stephan Gerhold wrote:
> >>>> Most of the reserved firmware memory on MSM8916 can be relocated when
> >>>> respecting the required alignment. To avoid having to precompute the
> >>>> reserved memory regions in every board DT, describe the actual
> >>>> requirements (size, alignment, alloc-ranges) using the dynamic reserved
> >>>> memory allocation.
> >>>>
> >>>> This approach has several advantages:
> >>>>
> >>>>   1. We can define "templates" for the reserved memory regions in
> >>>>      msm8916.dtsi and keep only device-specific details in the board DT.
> >>>>      This is useful for the "mpss" region size for example, which varies
> >>>>      from device to device. It is no longer necessary to redefine all
> >>>>      firmware regions to shift their addresses.
> >>>>
> >>>>   2. When some of the functionality (e.g. WCNSS, Modem, Venus) is not
> >>>>      enabled or needed for a device, the reserved memory can stay
> >>>>      disabled, freeing up the unused reservation for Linux.
> >>>>
> >>>>   3. Devices with special requirements for one of the firmware regions
> >>>>      are handled automatically. For example, msm8916-longcheer-l8150
> >>>>      has non-relocatable "wcnss" firmware that must be loaded exactly
> >>>>      at address 0x8b600000. When this is defined as a static region,
> >>>>      the other dynamic allocations automatically adjust to a different
> >>>>      place with suitable alignment.
> >>>>
> >>>> All in all this approach significantly reduces the boilerplate necessary
> >>>> to define the different firmware regions, and makes it easier to enable
> >>>> functionality on the different devices.
> >>>>
> >>>> Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
> >>>> ---
> >>> [...]
> >>>
> >>>>   		mpss_mem: mpss@86800000 {
> >>>> +			/*
> >>>> +			 * The memory region for the mpss firmware is generally
> >>>> +			 * relocatable and could be allocated dynamically.
> >>>> +			 * However, many firmware versions tend to fail when
> >>>> +			 * loaded to some special addresses, so it is hard to
> >>>> +			 * define reliable alloc-ranges.
> >>>> +			 *
> >>>> +			 * alignment = <0x0 0x400000>;
> >>>> +			 * alloc-ranges = <0x0 0x86800000 0x0 0x8000000>;
> >>>> +			 */
> >>> Do we know of any devices that this would actually work on?
> [...]
> >  - On DB410c it works just fine. All addresses I tried work without any
> >    problems.
> > 
> >  - On longcheer-l8150 the modem firmare works fine when the memory
> >    region starts somewhere between 0x86800000 and 0x8a800000. It also
> >    works again after 0x8e800000. But on anything between 0x8a800000 and
> >    0x8e800000 it's broken for who knows what reason.
> > [...]
> Were you able to find a phone (likely a very reference-design-based
> one) that this worked on, btw?

Actually I would count the Longcheer devices (l8150 = Wileyfox Swift and
l8910 = BQ Aquaris X5) to the category of close-to-QRD-based devices.
Based on quick tests both behave like described above (only
0x8a800000-0x8e800000 is broken). Same for wingtech-wt88047.

In other words, for those using the dynamic allocation would work fine,
because the alloc-ranges = <0x0 0x86800000 0x0 0x8000000>; only includes
working start addresses from 0x86800000 to ~0x89800000 (with a size of
0x5000000).

I guess I could use it for them and only make other devices use a fixed
address. But I also don't quite have the capacity to test every device
to see if relocating the region works or not.

I think it's still easiest to allocate mpss on a fixed address
everywhere. The only real disadvantage is that overriding "reg", e.g.

	&mpss_mem {
		reg = <0x0 0x86800000 0x0 0x5100000>;
	};

is a bit more ugly than overriding size:

	&mpss_mem {
		size = <0x0 0x5100000>;
	};

but well, this is a very minor disadvantage.

Thanks,
Stephan