Re: [PATCH v1 2/3] riscv: cache: Add CBO instructions

[Conor Dooley <conor.dooley@microchip.com>]

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On Tue, Aug 20, 2024 at 02:14:01PM +0200, Heinrich Schuchardt wrote:
> On 20.08.24 11:37, Mayuresh Chitale wrote:
> > +void riscv_zicbom_init(void)
> > +{
> > +	struct udevice *dev;
> > +
> > +	if (!CONFIG_IS_ENABLED(RISCV_ISA_ZICBOM))
> > +		return;
> > +
> > +	uclass_first_device(UCLASS_CPU, &dev);
> > +	if (!dev) {
> > +		log_err("Failed to get cpu device!\n");
> > +		return;
> 
> Please, return an error code.
> 
> > +	}
> > +
> > +	(void)dev_read_u32(dev, "riscv,cbom-block-size", &zicbom_block_size);
> 
> Please, do not ignore errors.

I'm curious what the policy of U-Boot is w.r.t. extension probing. Is it
okay to enable the option for Zicbom even if your hardware does not
support it, in which case riscv_zicbom_init() would be expected to fail
gracefully and no CMOs done?
Say, for example, you had two very similar chips, one with DMA non-coherent
peripherals and one that only differed by having DMA coherent ones, and you
wanted to run the same U-Boot binary on both devices using a devicetree
passed from firmware.

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