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Message-ID: <1e15c452-f8be-85fa-e424-b7463cc703eb@intel.com>
Date: Thu, 1 Jul 2021 11:34:49 +0300
From: "Neftin, Sasha" <sasha.neftin@...el.com>
To: Yee Li <seven.yi.lee@...il.com>
Cc: jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
davem@...emloft.net, kuba@...nel.org,
intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org,
"Ruinskiy, Dima" <dima.ruinskiy@...el.com>,
"Edri, Michael" <michael.edri@...el.com>,
"Efrati, Nir" <nir.efrati@...el.com>,
"Neftin, Sasha" <sasha.neftin@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH] driver core: fix e1000e ltr bug
On 6/30/2021 09:26, Yee Li wrote:
> I agree with you.
> That's better code.
Thank Yee-Li for discovering this problem. I would suggest we (intel)
will process a patch to address this problem. Can I put you kindly as
"Suggested-by"?
>
> Neftin, Sasha <sasha.neftin@...el.com <mailto:sasha.neftin@...el.com>>
> 于2021年6月30日周三 下午2:13写道：
>
> On 6/29/2021 20:33, Yee Li wrote:
> >
> > Yes, 18874368ns > 3145728ns.
> > But, 0xe40 < 0x1003.
> I got you. I would agree, direct comparison is error-prone. (10M is
> impacted)
> I would suggest do not use convert function. lat_en should rather
> presented as lat_enc = scale x value:
> Introduce two u16 variables, u16 lat_enc_d and u16 max_ltr_enc_d;
>
> lat_enc_d = (lat_enc & 0x0x3ff) x (1U << 5*((max_ltr_enc & 0x1c00)
> >> 10))
>
> max_ltr_enc_d = (max_ltr_enc & 0x0x3ff) x (1U << 5*((max_ltr_enc &
> 0x1c00) >> 10))
>
> Then:
> if (lat_enc_d > max_ltr_enc_d)
> lat_enc = max_ltr_enc;
> what do you think?
>
> >
> > So, the final lat_enc is 0xe40.
> > (Latency encoded is less than maximum LTR encoded by platform)
> >
> > Neftin, Sasha <sasha.neftin@...el.com
> <mailto:sasha.neftin@...el.com> <mailto:sasha.neftin@...el.com
> <mailto:sasha.neftin@...el.com>>>
> > 于 2021年6月29日周二 22:49写道：
> >
> > On 6/29/2021 11:21, YeeLi wrote:
> > Yeeli,
> > > In e1000e driver, a PCIe-like device, the max
> snoop/no-snoop latency
> > > is the upper limit.So, directly compare the size of
> lat_enc and
> > > max_ltr_enc is incorrect.
> > >
> > why?
> > > In 1000Mbps, 0x8b9 < 0x1003, 189440 ns < 3145728 ns,
> correct.
> > >
> > > In 100Mbps, 0xc3a < 0x1003, 1900544 ns < 3145728 ns,
> correct.
> > >
> > > In 10Mbps, 0xe40 < 0x1003, 18874368 > 3145728, incorrect.
> > >
> > Platform LTR encoded is 0x1003 - right. It is meant 1048576ns
> x 3 =
> > 3145738ns.
> > Now,
> > for 1000M: 0x08b9 => 185ns x 1024 = 189440ns (you are correct)
> > for 100M: 0x0c3a => 58ns x 32768 = 1900544ns (correct)
> > for 10M: 0x0e41 => 577ns x 32768 = 18907136ns (ok?)
> > 18907136ns > 3145738ns, (latency encoded is great than
> maximum LTR
> > encoded by platform) - so, there is no point to wait more
> than platform
> > required, and lat_enc=max_ltr_enc. It is expected and we sent
> right
> > value to the power management controller.
> > What is the problem you try solve?
> >
> > > Decoded the lat_enc and max_ltr_enc before compare them is
> necessary.
> > >
> > > Signed-off-by: YeeLi <seven.yi.lee@...il.com
> <mailto:seven.yi.lee@...il.com>
> > <mailto:seven.yi.lee@...il.com <mailto:seven.yi.lee@...il.com>>>
> > > ---
> > > drivers/net/ethernet/intel/e1000e/ich8lan.c | 23
> > ++++++++++++++++++++-
> > > 1 file changed, 22 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/net/ethernet/intel/e1000e/ich8lan.c
> > b/drivers/net/ethernet/intel/e1000e/ich8lan.c
> > > index 590ad110d383..3bff1b570b76 100644
> > > --- a/drivers/net/ethernet/intel/e1000e/ich8lan.c
> > > +++ b/drivers/net/ethernet/intel/e1000e/ich8lan.c
> > > @@ -986,6 +986,27 @@ static s32
> e1000_k1_workaround_lpt_lp(struct
> > e1000_hw *hw, bool link)
> > > return ret_val;
> > > }
> > >
> > > +static u32 convert_e1000e_ltr_scale(u32 val)
> > > +{
> > > + if (val > 5)
> > > + return 0;
> > > +
> > > + return 1U << (5 * val);
> > > +}
> > > +
> > > +static u64 decoded_ltr(u32 val)
> > > +{
> > > + u64 decoded_latency;
> > > + u32 value;
> > > + u32 scale;
> > > +
> > > + value = val & 0x03FF;
> > > + scale = (val & 0x1C00) >> 10;
> > > + decoded_latency = value *
> convert_e1000e_ltr_scale(scale);
> > > +
> > > + return decoded_latency;
> > > +}
> > > +
> > > /**
> > > * e1000_platform_pm_pch_lpt - Set platform power
> management
> > values
> > > * @hw: pointer to the HW structure
> > > @@ -1059,7 +1080,7 @@ static s32
> e1000_platform_pm_pch_lpt(struct
> > e1000_hw *hw, bool link)
> > > E1000_PCI_LTR_CAP_LPT + 2,
> > &max_nosnoop);
> > > max_ltr_enc = max_t(u16, max_snoop,
> max_nosnoop);
> > >
> > > - if (lat_enc > max_ltr_enc)
> > > + if (decoded_ltr(lat_enc) >
> decoded_ltr(max_ltr_enc))
> > > lat_enc = max_ltr_enc;
> > > }
> > >
> > >
> > sasha
> >
>
sasha
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