Re: [PATCH 3/3] arm: mach-imx: tzasc: convert to cpu_is_mx8xyz macros

[Stefan Kerkmann <s.kerkmann@pengutronix.de>]

Hi Sascha,

On 28.02.24 12:05, Sascha Hauer wrote:
> On Wed, Feb 28, 2024 at 09:46:51AM +0100, Stefan Kerkmann wrote:
>> Hi Sascha,
>>
>> On 27.02.24 09:44, Sascha Hauer wrote:
>>> On Mon, Feb 26, 2024 at 03:40:23PM +0100, Stefan Kerkmann wrote:
>>>> Instead of passing in configuration parameters at runtime we can utilize
>>>> the `cpu_is_mx8xyz` macro family to determine which bits should be set.
>>>>
>>>> As the tzasc driver is imx specific, all functions are prefixed with
>>>> `imx8m_` as well.
>>>>
>>>> Signed-off-by: Stefan Kerkmann <s.kerkmann@pengutronix.de>
>>>> ---
>>>>   arch/arm/mach-imx/atf.c   |  8 ++++----
>>>>   arch/arm/mach-imx/imx8m.c |  2 +-
>>>>   arch/arm/mach-imx/tzasc.c | 25 +++++--------------------
>>>>   include/mach/imx/tzasc.h  |  8 ++------
>>>>   4 files changed, 12 insertions(+), 31 deletions(-)
>>>>
>>>> diff --git a/arch/arm/mach-imx/atf.c b/arch/arm/mach-imx/atf.c
>>>> index e8060ebd95..9cbc38ef11 100644
>>>> --- a/arch/arm/mach-imx/atf.c
>>>> +++ b/arch/arm/mach-imx/atf.c
>>>> @@ -158,7 +158,7 @@ __noreturn void __imx8mm_load_and_start_image_via_tfa(void *bl33)
>>>>   		size_t bl32_size;
>>>>   		void *bl32_image;
>>>> -		imx8mm_tzc380_init();
>>>> +		imx8m_tzc380_init();
>>>
>>> I am not so sure about this patch. So far the whole PBL is coded in the
>>> way that we inherently know the SoC type from the code path chosen.
>>>
>>> This patch changes this. It doesn't really matter for this patch, but it
>>> sends a sign how we want to solve this in future.
>>
>> Let's see if I can persuade you that this is a good thing :-).
>>
>>> One implication of this patch is that cpu_is_mx() is a runtime decision,
>>> so code paths behind an unused cpu_is_mx() can't be discarded anymore.
>>
>> My argument here is that the overhead in code size is probably neglect able
>> in most cases, as most of the code paths are still discarded:
>>
>> 1. If there is only one ARCH selected e.g., `CONFIG_ARCH_IMX8MM` the
>> `cpu_is_mx8mm()` macro is still evaluated at compile time. As the
>> `__imx_cpu_type` variable is only assigned and never read it can be stripped
>> away by the compiler/linker and become a nop.
>>
>> 2. Runtime evaluation is only selected if a second arch is enabled for the
>> build. But even then the runtime decision is only compiled in for the two
>> selected arches, as all other `cpu_is_xyz` macros still evaluate at compile
>> time to false. So code paths that don't touch the selected arches will still
>> be stripped.
>>
>>> Another thing is that the usage of cpu_is() has the tendency to lead to
>>> cascades of if (cpu_is_x() || cpu_is_y() || cpu_is_z()) which is not
>>> paticularly nice to read.
>>>
>>
>> That is arguably subjective :-).
>>
>> For me as a developer that is new to barebox, it was confusing to find two
>> different styles of arch dependent code. I prefer the `cpu_is_xyz` style
>> approach which is used in barebox proper much more.
>>
>> In the case of the TZC380 driver the pseudo (as they are probably optimized
>> away) runtime arguments to the init functions seem unnecessarily
>> complicated, as does the approach to define aliases to the same function for
>> all arches. The if style is clearer in intend as it keeps the distinction
>> between the arches local to the parts that are actually different. Which is
>> straight forward to read IMHO.
> 
> Ok, let's see where this brings us. Can you rebase on current next?
> Some of the code you are modifying went to drivers/soc/imx/soc-imx8m.c
> recently.
> 

Great :-)! I've rebased and sent a v2 of this patch set.

> Sascha
> 

Cheers,
Stefan

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