Re: [PATCH 3/4] MIPS: cpu-probe: Set the write-combine CCA value on per core basis

[Florian Fainelli <f.fainelli@gmail.com>]

Hi Markos,

On 07/18/2014 02:51 AM, Markos Chandras wrote:
> Different cores use different CCA values to achieve write-combine
> memory writes. For cores that do not support write-combine we
> set the default value to CCA:2 (uncached, non-coherent) which is the
> default value as set by the kernel.
> 
> Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
> ---
[snip]
			break;
> @@ -765,67 +767,83 @@ static inline void cpu_probe_legacy(struct cpuinfo_mips *c, unsigned int cpu)
>  
>  static inline void cpu_probe_mips(struct cpuinfo_mips *c, unsigned int cpu)
>  {
> +	c->writecombine = _CACHE_UNCACHED_ACCELERATED;

Why do we set this writecombine setting by default, when later we are
going to override writecombine on a per-cpu basic.

In the end, we have the following:

cpu_probe()
	c->writecombine = _CACHE_UNCACHED;

	cpu_probe_mips()
		c->writecombine = _CACHE_UNCACHED_ACCELERATED:
		... per-cpu case ...
		c->writecombine = _CACHE_UNCACHED;

Can't we just eliminate the various assignments in cpu_probe_mips() and
only override c->writecombine if _CACHE_UNCACHED is not suitable?


>  	switch (c->processor_id & PRID_IMP_MASK) {
>  	case PRID_IMP_4KC:
>  		c->cputype = CPU_4KC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 4Kc";
>  		break;
>  	case PRID_IMP_4KEC:
>  	case PRID_IMP_4KECR2:
>  		c->cputype = CPU_4KEC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 4KEc";
>  		break;
>  	case PRID_IMP_4KSC:
>  	case PRID_IMP_4KSD:
>  		c->cputype = CPU_4KSC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 4KSc";
>  		break;
>  	case PRID_IMP_5KC:
>  		c->cputype = CPU_5KC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 5Kc";
>  		break;
>  	case PRID_IMP_5KE:
>  		c->cputype = CPU_5KE;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 5KE";
>  		break;
>  	case PRID_IMP_20KC:
>  		c->cputype = CPU_20KC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 20Kc";
>  		break;
>  	case PRID_IMP_24K:
>  		c->cputype = CPU_24K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 24Kc";
>  		break;
>  	case PRID_IMP_24KE:
>  		c->cputype = CPU_24K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 24KEc";
>  		break;
>  	case PRID_IMP_25KF:
>  		c->cputype = CPU_25KF;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 25Kc";
>  		break;
>  	case PRID_IMP_34K:
>  		c->cputype = CPU_34K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 34Kc";
>  		break;
>  	case PRID_IMP_74K:
>  		c->cputype = CPU_74K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 74Kc";
>  		break;
>  	case PRID_IMP_M14KC:
>  		c->cputype = CPU_M14KC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS M14Kc";
>  		break;
>  	case PRID_IMP_M14KEC:
>  		c->cputype = CPU_M14KEC;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS M14KEc";
>  		break;
>  	case PRID_IMP_1004K:
>  		c->cputype = CPU_1004K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 1004Kc";
>  		break;
>  	case PRID_IMP_1074K:
>  		c->cputype = CPU_1074K;
> +		c->writecombine = _CACHE_UNCACHED;
>  		__cpu_name[cpu] = "MIPS 1074Kc";
>  		break;
>  	case PRID_IMP_INTERAPTIV_UP:
> @@ -899,6 +917,7 @@ static inline void cpu_probe_sibyte(struct cpuinfo_mips *c, unsigned int cpu)
>  {
>  	decode_configs(c);
>  
> +	c->writecombine = _CACHE_UNCACHED_ACCELERATED;
>  	switch (c->processor_id & PRID_IMP_MASK) {
>  	case PRID_IMP_SB1:
>  		c->cputype = CPU_SB1;
> @@ -1030,6 +1049,7 @@ static inline void cpu_probe_ingenic(struct cpuinfo_mips *c, unsigned int cpu)
>  	switch (c->processor_id & PRID_IMP_MASK) {
>  	case PRID_IMP_JZRISC:
>  		c->cputype = CPU_JZRISC;
> +		c->writecombine = _CACHE_UNCACHED_ACCELERATED;
>  		__cpu_name[cpu] = "Ingenic JZRISC";
>  		break;
>  	default:
> @@ -1136,6 +1156,7 @@ void cpu_probe(void)
>  	c->processor_id = PRID_IMP_UNKNOWN;
>  	c->fpu_id	= FPIR_IMP_NONE;
>  	c->cputype	= CPU_UNKNOWN;
> +	c->writecombine = _CACHE_UNCACHED;



>  
>  	c->processor_id = read_c0_prid();
>  	switch (c->processor_id & PRID_COMP_MASK) {
>