[PATCH] driver core: fix e1000e ltr bug

[PATCH] driver core: fix e1000e ltr bug

[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.

    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.

Decoded the lat_enc and max_ltr_enc before compare them is necessary.

Signed-off-by: YeeLi <seven.yi.lee@gmail.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;
 	}
 
-- 
2.25.1

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

[Neftin, Sasha]

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@gmail.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

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

[Neftin, Sasha]

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@intel.com <mailto:sasha.neftin@intel.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@gmail.com
>     <mailto:seven.yi.lee@gmail.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
>

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@intel.com <mailto:sasha.neftin@intel.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@intel.com
>     <mailto:sasha.neftin@intel.com> <mailto:sasha.neftin@intel.com
>     <mailto:sasha.neftin@intel.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@gmail.com
>     <mailto:seven.yi.lee@gmail.com>
>      >     <mailto:seven.yi.lee@gmail.com <mailto:seven.yi.lee@gmail.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