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From: Andrew Jeffery <andrew@aj.id.au>
To: Christopher Bostic <cbostic@linux.vnet.ibm.com>,
 Benjamin Herrenschmidt <benh@kernel.crashing.org>, openbmc@lists.ozlabs.org
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References: <20180508010640.14113-1-benh@kernel.crashing.org>
 <05e89ea8549634e750d783360590f2802954437d.camel@kernel.crashing.org>
 <f2a71866-7ab5-8017-0865-14f4e9b57b91@linux.vnet.ibm.com>
In-Reply-To: <f2a71866-7ab5-8017-0865-14f4e9b57b91@linux.vnet.ibm.com>
Date: Thu, 10 May 2018 12:36:33 +0930
Subject: Re: [PATCH linux dev-4.13 6/6] fsi/fsi-master-gpio: Reduce dpoll
 clocks
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On Wed, 9 May 2018, at 05:30, Christopher Bostic wrote:
> Reviewed-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
> 
> 
> On 5/7/18 8:46 PM, Benjamin Herrenschmidt wrote:
> > FSI_GPIO_DPOLL_CLOCKS is the number of clocks before sending
> > a DPOLL command after receiving a BUSY status. It should be
> > at least tSendDelay (16 clocks).
> >
> > According to comments in the code, it needs to also be at least
> > 21 clocks due to HW issues.
> >
> > It's currently 100 clocks which impacts performances negatively
> > in some cases. Reduces it in half to 50 clocks which seems to
> > still be solid.

Out of curiosity, was there any science to 50 beyond the (16/21 cycle) reasoning above? Was there instability at lower values?

> >
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >   drivers/fsi/fsi-master-gpio.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
> > index 029b0a5b6d89..bd2b2cbd5eb5 100644
> > --- a/drivers/fsi/fsi-master-gpio.c
> > +++ b/drivers/fsi/fsi-master-gpio.c
> > @@ -29,7 +29,8 @@
> >   #define	FSI_GPIO_CMD_TERM	0x3f
> >   #define FSI_GPIO_CMD_ABS_AR	0x4
> >
> > -#define	FSI_GPIO_DPOLL_CLOCKS	100      /* < 21 will cause slave to hang */
> > +
> > +#define	FSI_GPIO_DPOLL_CLOCKS	50      /* < 21 will cause slave to hang */
> >
> >   /* Bus errors */
> >   #define	FSI_GPIO_ERR_BUSY	1	/* Slave stuck in busy state */
> > @@ -43,7 +44,7 @@
> >   #define	FSI_GPIO_RESP_ACK	0
> >   #define	FSI_GPIO_RESP_ACKD	4
> >
> > -#define	FSI_GPIO_MAX_BUSY	100
> > +#define	FSI_GPIO_MAX_BUSY	200
> >   #define	FSI_GPIO_MTOE_COUNT	1000
> >   #define	FSI_GPIO_DRAIN_BITS	20
> >   #define	FSI_GPIO_CRC_SIZE	4
> >
>