Re: [PATCH] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc

[Timur Tabi]

Will Deacon wrote:
> On Fri, Jun 19, 2015 at 11:08:54PM +0100, Timur Tabi wrote:
> > From: Abhimanyu Kapur <abhimany@xxxxxxxxxxxxxx>
> >
> > Add support for debug communications channel based
> > hvc console for arm64 cpus.
>
> I still think we should be disabling userspace access to the DCC if the
> kernel is using it as its console.

I don't disagree, I just don't know how to do that.

> > + * A call to __dcc_getchar() or __dcc_putchar() is typically followed by
> > + * a call to __dcc_getstatus().  We want to make sure that the CPU does
> > + * not speculative read the DCC status before executing the read or write
> > + * instruction.  That's what the ISBs are for.
> > + *
> > + * The 'volatile' ensures that the compiler does not cache the status bits,
> > + * and instead reads the DCC register every time.
> > + */
>
> Missing header guards.

Will fix.

> > +#include <asm/barrier.h>
> > +
> > +static inline u32 __dcc_getstatus(void)
> > +{
> > +	u32 __ret;
> > +
> > +	asm volatile("mrs %0, mdccsr_el0" : "=r" (__ret)
> > +			: : "cc");
>
> You don't need the "cc" clobber.

Will fix.

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