Re: [PATCH qemu] spapr: tune rtas-size

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jun 22, 2021 at 05:03:36PM +1000, Alexey Kardashevskiy wrote:
> QEMU reserves space for RTAS via /rtas/rtas-size which tells the client
> how much space the RTAS requires to work which includes the RTAS binary
> blob implementing RTAS runtime. Because pseries supports FWNMI which
> requires plenty of space, QEMU reserves more than 2KB which is
> enough for the RTAS blob as it is just 20 bytes (under QEMU).
> 
> Since FWNMI reset delivery was added, RTAS_SIZE macro is not used anymore.
> This replaces RTAS_SIZE with RTAS_MIN_SIZE and uses it in
> the /rtas/rtas-size calculation to account for the RTAS blob.
> 
> Fixes: 0e236d347790 ("ppc/spapr: Implement FWNMI System Reset delivery")
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Applied to ppc-for-6.1, thanks.

> ---
> 
> Alternatively SLOF could add hv_rtas_size to the property itself
> but splitting calculations between 2 chunks of code seems an overkill.
> The RTAS blob has always been 20 bytes and unlikely to ever change.
> ---
>  include/hw/ppc/spapr.h | 2 +-
>  hw/ppc/spapr.c         | 8 ++++++--
>  2 files changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index f05219f75ef6..5697327e4c00 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -770,7 +770,7 @@ void spapr_load_rtas(SpaprMachineState *spapr, void *fdt, hwaddr addr);
>  #define SPAPR_IS_PCI_LIOBN(liobn)   (!!((liobn) & 0x80000000))
>  #define SPAPR_PCI_DMA_WINDOW_NUM(liobn) ((liobn) & 0xff)
>  
> -#define RTAS_SIZE               2048
> +#define RTAS_MIN_SIZE           20 /* hv_rtas_size in SLOF */
>  #define RTAS_ERROR_LOG_MAX      2048
>  
>  /* Offset from rtas-base where error log is placed */
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 4dd90b75cc52..9e19c570327e 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -919,9 +919,13 @@ static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
>       *
>       * The extra 8 bytes is required because Linux's FWNMI error log check
>       * is off-by-one.
> +     *
> +     * RTAS_MIN_SIZE is required for the RTAS blob itself.
>       */
> -    _FDT(fdt_setprop_cell(fdt, rtas, "rtas-size", RTAS_ERROR_LOG_MAX +
> -			  ms->smp.max_cpus * sizeof(uint64_t)*2 + sizeof(uint64_t)));
> +    _FDT(fdt_setprop_cell(fdt, rtas, "rtas-size", RTAS_MIN_SIZE +
> +                          RTAS_ERROR_LOG_MAX +
> +                          ms->smp.max_cpus * sizeof(uint64_t) * 2 +
> +                          sizeof(uint64_t)));
>      _FDT(fdt_setprop_cell(fdt, rtas, "rtas-error-log-max",
>                            RTAS_ERROR_LOG_MAX));
>      _FDT(fdt_setprop_cell(fdt, rtas, "rtas-event-scan-rate",

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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