[Skiboot] [PATCH] capi: Enable channel tag streaming for PHB in CAPP mode

[Andrew Donnellan]

On 31/01/18 17:52, Vaibhav Jain wrote:
> We re-enable channel tag streaming for PHB in CAPP mode as without it
> PEC was waiting for cresp for each DMA write command before sending a
> new DMA write command on the Powerbus. This resulted in much lower DMA
> write performance than expected.
> 
> The patch updates enable_capi_mode() to remove the masking of
> channel_streaming_en bit in PBCQ Hardware Configuration Register. Also
> does some re-factoring of the code that updates this register to use
> xscom_write_mask instead of xscom_read followed by a xscom_write.
> 
> Cc: stable
> Signed-off-by: Vaibhav Jain <vaibhav at linux.vnet.ibm.com>

Reviewed-by: Andrew Donnellan <andrew.donnellan at au1.ibm.com>

> ---
>   hw/phb4.c | 12 ++++--------
>   1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/phb4.c b/hw/phb4.c
> index ff912e1f..4906caf4 100644
> --- a/hw/phb4.c
> +++ b/hw/phb4.c
> @@ -3793,14 +3793,10 @@ static int64_t enable_capi_mode(struct phb4 *p, uint64_t pe_number,
>   	reg |= dma_eng;
>   	xscom_write(p->chip_id, p->pe_xscom + XPEC_NEST_CAPP_CNTL, reg);
> 
> -	/* PCI to PB data movement ignores the PB init signal.
> -	 * Disable streaming.
> -	 */
> -	xscom_read(p->chip_id, p->pe_xscom + XPEC_NEST_PBCQ_HW_CONFIG, &reg);
> -	reg |= XPEC_NEST_PBCQ_HW_CONFIG_PBINIT;
> -	if (p->index == CAPP0_PHB_INDEX)
> -		reg &= ~XPEC_NEST_PBCQ_HW_CONFIG_CH_STR;
> -	xscom_write(p->chip_id, p->pe_xscom + XPEC_NEST_PBCQ_HW_CONFIG, reg);
> +	/* PCI to PB data movement ignores the PB init signal. */
> +	xscom_write_mask(p->chip_id, p->pe_xscom + XPEC_NEST_PBCQ_HW_CONFIG,
> +			 XPEC_NEST_PBCQ_HW_CONFIG_PBINIT,
> +			 XPEC_NEST_PBCQ_HW_CONFIG_PBINIT);
> 
>   	/* PEC Phase 4 (PHB) registers adjustment
>   	 * Inbound CAPP traffic: The CAPI can send both CAPP packets and
> 

-- 
Andrew Donnellan              OzLabs, ADL Canberra
andrew.donnellan at au1.ibm.com  IBM Australia Limited