Re: [PATCH 3/6] arm64: tegra: Add Tegra210 support

[Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>]

On 05/22/2015 07:38 AM, Catalin Marinas wrote:
> On Tue, May 19, 2015 at 05:17:42PM +0200, Thierry Reding wrote:
>> On Tue, May 19, 2015 at 03:52:11PM +0100, Catalin Marinas wrote:
>>> On Fri, May 15, 2015 at 12:19:16PM +0200, Thierry Reding wrote:
>>>> On Wed, May 13, 2015 at 06:11:15PM +0100, Catalin Marinas wrote:
>>>>> On Wed, May 13, 2015 at 04:57:42PM +0200, Thierry Reding wrote:
>>>>>> From: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>>>>
>>>>>> NVIDIA Tegra210 (also known as Tegra X1) has four Cortex-A57 and four
>>>>>> Cortex-A53 CPUs. Compared to Tegra124 and Tegra132 it comes with a 256-
>>>>>> core Maxwell GPU. It supports processing videos of up to 4K resolutions
>>>>>> at 60 fps (H.265, VP9, H.264).
>>>>>>
>>>>>> Signed-off-by: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>>>>>> ---
>>>>>>   arch/arm64/Kconfig                       |   9 +
>>>>>>   arch/arm64/boot/dts/nvidia/tegra210.dtsi | 998 +++++++++++++++++++++++++++++++
>>>>>>   2 files changed, 1007 insertions(+)
>>>>>>   create mode 100644 arch/arm64/boot/dts/nvidia/tegra210.dtsi
>>>>>>
>>>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>>>>> index 7796af4b1d6f..bfdf064ada66 100644
>>>>>> --- a/arch/arm64/Kconfig
>>>>>> +++ b/arch/arm64/Kconfig
>>>>>> @@ -225,6 +225,15 @@ config ARCH_TEGRA_132_SOC
>>>>>>   	  but contains an NVIDIA Denver CPU complex in place of
>>>>>>   	  Tegra124's "4+1" Cortex-A15 CPU complex.
>>>>>>
>>>>>> +config ARCH_TEGRA_210_SOC
>>>>>> +	bool "NVIDIA Tegra210 SoC"
>>>>>> +	depends on ARCH_TEGRA
>>>>>> +	select PINCTRL_TEGRA210
>>>>>> +	select USB_ULPI if USB_PHY
>>>>>> +	select USB_ULPI_VIEWPORT if USB_PHY
>>>>>> +	help
>>>>>> +	  Enable support for the NVIDIA Tegra210 SoC.
>>>>>> +
>>>>>
>>>>> The previous ARCH_TEGRA_132_SOC escaped me. Do we need all these
>>>>> ARCH_TEGRA_*_SOC entries? Can we not have per-driver Kconfig options?
>>>>> For example, ARCH_TEGRA_132_SOC seems to be only used in
>>>>> drivers/clk/tegra, a specific Kconfig entry in there would suffice.
>>>>
>>>> There are actually a couple of other places where this will be used in
>>>> subsequent patches (e.g. memory controller driver). The idea behind
>>>> having these is that each one of them is used to enable the essentials
>>>> out of the box, so that people don't have to go and enable a bunch of
>>>> driver-specific Kconfig options just to get a kernel configuration that
>>>> can actually boot.
>>>
>>> We debated whether to have ARCH_* options at all on arm64 and we settled
>>> for the middle ground - only add them for SoC families, not individual
>>> SoCs. As for the kernel configuration that actually boots, we want the
>>> arm64 defconfig to include all the supported SoCs and drivers (though
>>> longer term I'd like to see more drivers built as modules by default).
>>>
>>>> This is also useful for integrators since they can simply omit all SoC
>>>> generations that they're not interested in. Having a per-SoC option
>>>> provides an easy way of doing so.
>>>
>>> The integrators could just select a SoC family and trim down unwanted
>>> options, I don't think they rely on the kernel defconfig for a final
>>> product. If this becomes an issue, I would rather have per-SoC
>>> defconfigs than lots of Kconfig entries.
>>
>> I understand the desire to start with a clean plate on a new
>> architecture, but Tegra has worked like this for the past 5 years and
>> it's worked out really well for us. So I'm reluctant to introduce these
>> inconsistencies merely because 64-bit ARM now lives in a different
>> directory.
>
> That's a good time to start cleaning this up, especially since we
> mandate single image from the beginning.
>
>> Are you concerned about arch/arm64/Kconfig growing wild? If so we could
>> easily move these configuration options outside to something like
>> drivers/soc/tegra/Kconfig. While at it, we could move existing options
>> from arch/arm/mach-tegra over to that as well.
>
> I think the whole ARCH_TEGRA_*_SOC approach is wrong. You don't bother
> introducing Kconfig entries for individual drivers but instead add an
> obj-*_SOC in various Makefiles under drivers/. If we ever get to a point
> where we can build (part of) the SoCs as modules (and I'm not talking
> about kernels shipped with end products but those distro kernel
> targeting development boards), we have to go back and add such Kconfig
> entries for specific drivers.

Just as an aside, long long ago I tried to remove the ARCH_TEGRA_* usage 
from anywhere outside arch/arm/mach-tegra, but was shot down because 
that would not allow the driver Kconfig files to only show the drivers 
that were relevant for the particular Tegra SoCs we had enabled. It's 
really frustrating to have to deal with the situation of different 
people pushing in completely the opposite directions on this kind of topic.
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