Re: [Intel-wired-lan] [PATCH] driver core: fix e1000e ltr bug

[Neftin, Sasha]

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@xxxxxxxxx <mailto:sasha.neftin@xxxxxxxxx>> 
> 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@xxxxxxxxx
>     <mailto:sasha.neftin@xxxxxxxxx> <mailto:sasha.neftin@xxxxxxxxx
>     <mailto:sasha.neftin@xxxxxxxxx>>>
>      > 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@xxxxxxxxx
>     <mailto:seven.yi.lee@xxxxxxxxx>
>      >     <mailto:seven.yi.lee@xxxxxxxxx <mailto:seven.yi.lee@xxxxxxxxx>>>
>      >      > ---
>      >      >   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