Re: [PATCH] arc: Flush and invalidate caches on start

[Alexey Brodkin]

Hi Vineet,

On Thu, 2017-08-31 at 09:31 -0700, Vineet Gupta wrote:
> On 08/31/2017 07:22 AM, Alexey Brodkin wrote:
> > 
> > This is useful to make sure no stale data exists in caches after bootloaders.
> > The worst thing could be some lines of cache were locked in a bootloader
> > for example during DDR recalibration and never unlocked. This may lead
> > to really unpredictable issues later down the line.
> > 
> > Signed-off-by: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> > ---
> > Â arch/arc/kernel/head.S | 16 ++++++++++++++++
> > Â 1 file changed, 16 insertions(+)
> > 
> > diff --git a/arch/arc/kernel/head.S b/arch/arc/kernel/head.S
> > index 8b90d25a15cc..04e28b664183 100644
> > --- a/arch/arc/kernel/head.S
> > +++ b/arch/arc/kernel/head.S
> > @@ -34,6 +34,10 @@
> > Â #endif
> > ÂÂ	sr	r5, [ARC_REG_IC_CTRL]
> > ÂÂ
> > +	; Invalidate entire I$
> > +	mov	r5, 1
> > +	sr	r5, [ARC_REG_IC_IVIC]
> > +
> > Â 1:
> > ÂÂ	lr	r5, [ARC_REG_DC_BCR]
> > ÂÂ	breqÂÂÂÂr5, 0, 1f		; D$ doesn't exist
> > @@ -46,6 +50,18 @@
> > Â #endif
> > ÂÂ	sr	r5, [ARC_REG_DC_CTRL]
> > ÂÂ
> > +	; Flush entire D$
> > +	mov	r5, 1
> > +	sr	r5, [ARC_REG_DC_FLSH]
> > +	; Wait for flush operation to complete
> > +1:
> > +	lr	r5, [ARC_REG_DC_CTRL]
> > +	bbit1	r5, DC_CTRL_FLUSH_STATUS, 1b
> > +
> > +	; Invalidate entire D$
> > +	mov	r5, 1
> > +	sr	r5, [ARC_REG_DC_IVDC]
> > +
> 
> AFAIK uboot already flushes the caches before handing control over to kernel - soÂ
> why do we need it here.
> If uboot is locking lines, it needs to fix that and not penalize the general caseÂ
> with or w/o uboot !

U-Boot indeed flushes caches.. but doesn't invalidate them!
And only invalidation unlocks locked lines.

That indeed should be added in U-Boot but I'd say above stuff doesn't
influence a lot code size or execution time while makes system more fool-proof.

-Alexey