Re: [PATCH v4 09/10] powerpc/watchpoint: Return available watchpoints dynamically

On 7/21/20 5:06 PM, Michael Ellerman wrote:

Ravi Bangoria [off-list ref] writes:

quoted

On 7/20/20 9:12 AM, Jordan Niethe wrote:

quoted

On Fri, Jul 17, 2020 at 2:11 PM Ravi Bangoria
[off-list ref] wrote:

quoted

So far Book3S Powerpc supported only one watchpoint. Power10 is
introducing 2nd DAWR. Enable 2nd DAWR support for Power10.
Availability of 2nd DAWR will depend on CPU_FTR_DAWR1.

Signed-off-by: Ravi Bangoria <redacted>
---
   arch/powerpc/include/asm/cputable.h      | 4 +++-
   arch/powerpc/include/asm/hw_breakpoint.h | 5 +++--
   2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index 3445c86e1f6f..36a0851a7a9b 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h

@@ -633,7 +633,9 @@ enum {
    * Maximum number of hw breakpoint supported on powerpc. Number of
    * breakpoints supported by actual hw might be less than this.
    */
-#define HBP_NUM_MAX    1
+#define HBP_NUM_MAX    2
+#define HBP_NUM_ONE    1
+#define HBP_NUM_TWO    2

quoted

quoted

I wonder if these defines are necessary - has it any advantage over
just using the literal?

No, not really. Initially I had something like:

#define HBP_NUM_MAX    2
#define HBP_NUM_P8_P9  1
#define HBP_NUM_P10    2

But then I thought it's also not right. So I made it _ONE and _TWO.
Now the function that decides nr watchpoints dynamically (nr_wp_slots)
is in different file, I thought to keep it like this so it would be
easier to figure out why _MAX is 2.

I don't think it makes anything clearer.

I had to stare at it thinking there was some sort of mapping or
indirection going on, before I realised it's just literally the number
of breakpoints.

So please just do:

static inline int nr_wp_slots(void)
{
        return cpu_has_feature(CPU_FTR_DAWR1) ? 2 : 1;
}

If you think HBP_NUM_MAX needs explanation then do that with a comment,
it can refer to nr_wp_slots() if that's helpful.

Agreed. By adding a comment, we can remove those macros. Will change it.

Thanks,
Ravi