[U-Boot] [PATCH v4 16/25] riscv: Update supports_extension() to use desc from cpu driver

[Auer, Lukas]

Hi Bin,

On Tue, 2018-12-11 at 23:11 -0800, Bin Meng wrote:
> This updates supports_extension() implementation to use the desc
> string from the cpu driver whenever possible, which avoids the
> reading of misa CSR for S-mode U-Boot.
> 
> Signed-off-by: Bin Meng <bmeng.cn at gmail.com>
> 
> ---
> 
> Changes in v4:
> - print warnings for S-mode without CONFIG_CPU
> 
> Changes in v3:
> - new patch to update supports_extension() to use desc from cpu
> driver
> 
> Changes in v2: None
> 
>  arch/riscv/cpu/cpu.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
> index d3c59da..a2ebaf3 100644
> --- a/arch/riscv/cpu/cpu.c
> +++ b/arch/riscv/cpu/cpu.c
> @@ -5,8 +5,10 @@
>  
>  #include <common.h>
>  #include <cpu.h>
> +#include <dm.h>
>  #include <log.h>
>  #include <asm/csr.h>
> +#include <dm/uclass-internal.h>
>  
>  /*
>   * prior_stage_fdt_address must be stored in the data section since
> it is used
> @@ -16,7 +18,27 @@ phys_addr_t prior_stage_fdt_address
> __attribute__((section(".data")));
>  
>  static inline bool supports_extension(char ext)
>  {
> +#ifdef CONFIG_CPU
> +	struct udevice *dev;
> +	char desc[32];
> +
> +	uclass_find_first_device(UCLASS_CPU, &dev);

Sorry, I missed this before. Can you add error handling here to catch
uclass_find_first_device returning an error or not finding a device? It
would probably also make sense to print a warning message to the user
in this case.

Other than that, this patch and the series look good!
Reviewed-by: Lukas Auer <lukas.auer at aisec.fraunhofer.de>

Thanks,
Lukas

> +	if (!cpu_get_desc(dev, desc, sizeof(desc))) {
> +		/* skip the first 4 characters (rv32|rv64) */
> +		if (strchr(desc + 4, ext))
> +			return true;
> +	}
> +
> +	return false;
> +#else  /* !CONFIG_CPU */
> +#ifdef CONFIG_RISCV_MMODE
>  	return csr_read(misa) & (1 << (ext - 'a'));
> +#else  /* !CONFIG_RISCV_MMODE */
> +#warning "There is no way to determine the available extensions in
> S-mode."
> +#warning "Please convert your board to use the RISC-V CPU driver."
> +	return false;
> +#endif /* CONFIG_RISCV_MMODE */
> +#endif /* CONFIG_CPU */
>  }
>  
>  static int riscv_cpu_probe(void)