linux-kernel - [PATCH] driver core: fix e1000e ltr bug

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Date:   Tue, 29 Jun 2021 16:21:28 +0800
From:   YeeLi <seven.yi.lee@...il.com>
To:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     intel-wired-lan@...ts.osuosl.org, linux-kernel@...r.kernel.org,
        seven.yi.lee@...il.com
Subject: [PATCH] driver core: fix e1000e ltr bug

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@...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;
 	}
 
-- 
2.25.1