Re: [RFC , PATCH] support for the ibm,pa_features cpu property

[Will Schmidt <will_schmidt@vnet.ibm.com>]

Whoops.. funny thing occurred to me on my drive home..   comment inline

On Fri, 2006-04-28 at 13:41 -0500, Will Schmidt wrote:
> To determine if our processors support some features, such as large
> pages, we should be using the ibm,pa_features property, rather than just
> the PVR values.  
> This is an initial pass at the functionality.  This has been tested in
> the case where the property is missing, but still needs to be tested
> against a system where the property actually exists.  :-o  
> 
> 
> 
> diff --git a/arch/powerpc/kernel/setup_64.c
> b/arch/powerpc/kernel/setup_64.c
> index 13e91c4..78ad054 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -106,6 +106,65 @@ static struct notifier_block ppc64_panic
>  	.priority = INT_MIN /* may not return; must be done last */
>  };
> 
> +/*
> + * ibm,pa-features is a per-cpu property that contains a 2 byte header
> + * plus up to 256 bytes worth of processor attributes.  First header
> + * byte specifies the number of bytes implemented by the platform.
> + * Second header byte is an "attribute-specifier" type, which should
> + * be zero.  Remainder of the data consists of ones and zeros.
> + * Implementation:  Pass in the byte and bit offset for the feature
> + * that we are interested in.  The function will return -1 if the
> + * pa-features property is missing, or a 1/0 to indicate if the feature
> + * is supported/not supported.
> + */
> +
> +static int get_pa_features(int pabyte,int pabit)
> +{
> +	struct device_node *cpu;
> +	char *pa_feature_table;
> +
> +	cpu = of_find_node_by_type(NULL, "cpu");
> +	pa_feature_table = 
> +		(char *)get_property(cpu, "ibm,pa-features", NULL);
> +
> +	if ( pa_feature_table == NULL ) {
> +		printk("ibm,pa-features property is missing.\n");
> +		return -1;
> +	}
> +
> +	/* sanity check */
> +	if ( pabyte > pa_feature_table[0] ) {
> +		printk("%s: %d out of range for table of size %d\n",
> +			__FUNCTION__,pabyte,pa_feature_table[0]);
> +		return -1;
> +	}
> +	
> +	return pa_feature_table[2+pabyte*8+pabit];

pa_feature_table would be byte (char) addressable, while the fields that
we are interested with inside are actually bit values.  So this should
be something like

	return   (pa_feature_table[2+pabyte] & 1<<pabit);


> +}
> +
> +/*
> + * set values within the cur_cpu_spec table according to
> + * the ibm,pa_features property. 
> + * potential entries include: 
> + * Byte 0, bit 1 - FPU available
> + * Byte 1, bit 2 - Large Pages 
> + * Byte 2, bit 3 - DAR set on alignment Interrupt. 
> + */
> +static void add_cpu_features()
> +{
> +	/* if no property, bail early */
> +	if (get_pa_features(0,0) == -1 ) return;
> +
> +	if (get_pa_features(1,2) ) {
> +		printk("Adding CI_LARGE_PAGE to cur_cpu_spec \n");
> +		cur_cpu_spec->cpu_features |= CPU_FTR_CI_LARGE_PAGE;
> +	}
> +
> +	/* add more here... */
> +
> +}
> +
> +
>  #ifdef CONFIG_SMP
> 
>  static int smt_enabled_cmdline;
> @@ -425,6 +484,8 @@ void __init setup_system(void)
> 
>  	parse_early_param();
> 
> +	add_cpu_features();
> +
>  	check_smt_enabled();
>  	smp_setup_cpu_maps();
> 
> 
> 
> 
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev