[Skiboot] [PATCH v2 5/5] external: Update xscom utils for type 1 indirect accesses

[Cédric Le Goater]

On 03/23/2017 07:15 AM, Michael Neuling wrote:
> Update get/putscom utils to support type 1 indirect access.
> 
> Currently we do some (ugly) bit mangling so that we can fit a 64 bit
> scom address into the debugfs interface. The current code only shifts
> down the top bit (indirect bit). This patch changes it to shift down
> the whole top nibble so that the form of the indirection is also
> shifted.
> 
> Also currently putscom always reads back the value. This causes a
> problem for form 1 which can only be written.  This patch marks the
> form 1 as not readable and hence doesn't attempt the read back.
>
> The kernel debugfs scom driver doesn't do the bit mangling correctly.
> So for form1 to work correctly, the kernel debugfs scom driver needs
> updating. Existing scoms are forwards and backwards compatible with
> the kernel.
> 
> (FWIW the kernel PRD scom interface doesn't need to be updated as it
> passes the whole 64 bit scom address without any bit mangling)
>
> Signed-off-by: Michael Neuling <mikey at neuling.org>

Reviewed-by: Cédric Le Goater <clg at kaod.org>

Thanks,

C.

> ---
>  external/xscom-utils/putscom.c | 10 ++++++----
>  external/xscom-utils/xscom.c   | 21 +++++++++++++++++++--
>  external/xscom-utils/xscom.h   |  2 ++
>  3 files changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/external/xscom-utils/putscom.c b/external/xscom-utils/putscom.c
> index 7eaa59e8d1..ca8c0da305 100644
> --- a/external/xscom-utils/putscom.c
> +++ b/external/xscom-utils/putscom.c
> @@ -92,10 +92,12 @@ int main(int argc, char *argv[])
>  		fprintf(stderr,"Error %d writing XSCOM\n", rc);
>  		exit(1);
>  	}
> -	rc = xscom_read(chip_id, addr, &val);
> -	if (rc) {
> -		fprintf(stderr,"Error %d reading XSCOM\n", rc);
> -		exit(1);
> +	if (xscom_readable(addr)) {
> +		rc = xscom_read(chip_id, addr, &val);
> +		if (rc) {
> +			fprintf(stderr,"Error %d reading XSCOM\n", rc);
> +			exit(1);
> +		}
>  	}
>  	printf("%016" PRIx64 "\n", val);
>  	return 0;
> diff --git a/external/xscom-utils/xscom.c b/external/xscom-utils/xscom.c
> index 3338542b10..2425730334 100644
> --- a/external/xscom-utils/xscom.c
> +++ b/external/xscom-utils/xscom.c
> @@ -131,8 +131,17 @@ static struct xscom_chip *xscom_find_chip(uint32_t chip_id)
>  
>  static uint64_t xscom_mangle_addr(uint64_t addr)
>  {
> -	if (addr & (1ull << 63))
> -		addr |= (1ull << 59);
> +	uint64_t tmp;
> +
> +	/*
> +	 * Shift the top 4 bits (indirect mode) down by 4 bits so we
> +	 * don't lose going through the debugfs interfaces.
> +	 */
> +	tmp = (addr & 0xf000000000000000) >> 4;
> +	addr &= 0x00ffffffffffffff;
> +	addr |= tmp;
> +
> +	/* Shift up by 3 for debugfs */
>  	return addr << 3;
>  }
>  
> @@ -192,6 +201,14 @@ int xscom_write_ex(uint32_t ex_target_id, uint64_t addr, uint64_t val)
>  	return xscom_write(chip_id, addr, val);
>  }
>  
> +bool xscom_readable(uint64_t addr)
> +{
> +	/* Top nibble 9 indicates form 1 indirect, which is write only */
> +	if (((addr >> 60) & 0xf) == 9)
> +		return false;
> +	return true;
> +}
> +
>  uint32_t xscom_init(void)
>  {
>  	return xscom_scan_chips(XSCOM_BASE_PATH);
> diff --git a/external/xscom-utils/xscom.h b/external/xscom-utils/xscom.h
> index 52ba119bf3..5f9edbc9b3 100644
> --- a/external/xscom-utils/xscom.h
> +++ b/external/xscom-utils/xscom.h
> @@ -27,6 +27,8 @@ extern int xscom_write_ex(uint32_t ex_target_id, uint64_t addr, uint64_t val);
>  
>  extern void xscom_for_each_chip(void (*cb)(uint32_t chip_id));
>  
> +extern bool xscom_readable(uint64_t addr);
> +
>  extern uint32_t xscom_init(void);
>  
>  #endif /* __XSCOM_H */
>