Re: [PATCH] mips: scache: fix scache init with invalid line size.

[Govindraj Raja <govindraj.raja@xxxxxxxxxx>]

Hi James,

On 18/01/16 15:05, James Hogan wrote:
> Hi Govindraj,
>
> On Mon, Jan 18, 2016 at 02:18:26PM +0000, Govindraj Raja wrote:
>> In current scache init cache line_size is determined from
>> cpu config register, however if there there no scache
>> then mips_sc_probe_cm3 function populates a invalid line_size of 2.
>>
>> The invalid line_size can cause a NULL pointer deference
>> during r4k_dma_cache_inv as r4k_blast_scache is populated based on
>> line_size. Scache line_size of 2 is invalid option in r4k_blast_scache_setup.
>>
>> This issue was faced during a MIPS I6400 based virtual platform bring up
>> where scache was not available in virtual platform model.
>>
>> Signed-off-by: Govindraj Raja <Govindraj.Raja@xxxxxxxxxx>
>> ---
>>  arch/mips/mm/sc-mips.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/mips/mm/sc-mips.c b/arch/mips/mm/sc-mips.c
>> index 3bd0597..6e422bc 100644
>> --- a/arch/mips/mm/sc-mips.c
>> +++ b/arch/mips/mm/sc-mips.c
>> @@ -168,7 +168,8 @@ static int __init mips_sc_probe_cm3(void)
>>  
>>  	line_sz = cfg & CM_GCR_L2_CONFIG_LINE_SIZE_MSK;
>>  	line_sz >>= CM_GCR_L2_CONFIG_LINE_SIZE_SHF;
>> -	c->scache.linesz = 2 << line_sz;
>> +	if (line_sz)
>> +		c->scache.linesz = 2 << line_sz;
> It seems wrong to clear MIPS_CACHE_NOT_PRESENT if we know there isn't a
> cache actually present.
>
> Cheers
> James
>
>
Does this patch[1] makes sense?

I will repost v2 is its ok?

--
Thanks,
Govindraj.R

[1]:

diff --git a/arch/mips/mm/sc-mips.c b/arch/mips/mm/sc-mips.c
index 3bd0597..68c48f4 100644
--- a/arch/mips/mm/sc-mips.c
+++ b/arch/mips/mm/sc-mips.c
@@ -164,11 +164,13 @@ static int __init mips_sc_probe_cm3(void)
 
        sets = cfg & CM_GCR_L2_CONFIG_SET_SIZE_MSK;
        sets >>= CM_GCR_L2_CONFIG_SET_SIZE_SHF;
-       c->scache.sets = 64 << sets;
+       if (sets)
+               c->scache.sets = 64 << sets;
 
        line_sz = cfg & CM_GCR_L2_CONFIG_LINE_SIZE_MSK;
        line_sz >>= CM_GCR_L2_CONFIG_LINE_SIZE_SHF;
-       c->scache.linesz = 2 << line_sz;
+       if (line_sz)
+               c->scache.linesz = 2 << line_sz;
 
        assoc = cfg & CM_GCR_L2_CONFIG_ASSOC_MSK;
        assoc >>= CM_GCR_L2_CONFIG_ASSOC_SHF;
@@ -176,7 +178,8 @@ static int __init mips_sc_probe_cm3(void)
        c->scache.waysize = c->scache.sets * c->scache.linesz;
        c->scache.waybit = __ffs(c->scache.waysize);
 
-       c->scache.flags &= ~MIPS_CACHE_NOT_PRESENT;
+       if (c->scache.linesz)
+               c->scache.flags &= ~MIPS_CACHE_NOT_PRESENT;
 
        return 1;
 }