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

[Sascha Hauer <s.hauer@pengutronix.de>]

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.

Sascha

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