issue with unreachable code in net sxgbe driver

From: Colin Ian King
Date: Fri Jul 09 2021 - 10:03:38 EST


Hi,

Static analysis with Coverity has detected several occurrences of dead
code in the sxgbe driver in function sxgbe_mtl_init. The issue was
introduced with the following commit:

commit 1edb9ca69e8a7988900fc0283e10550b5592164d
Author: Siva Reddy <siva.kallam@xxxxxxxxxxx>
Date: Tue Mar 25 12:10:54 2014 -0700

net: sxgbe: add basic framework for Samsung 10Gb ethernet driver

The analysis is as follows:

20static void sxgbe_mtl_init(void __iomem *ioaddr, unsigned int etsalg,
21 unsigned int raa)
22{
23 u32 reg_val;
24
25 reg_val = readl(ioaddr + SXGBE_MTL_OP_MODE_REG);
26 reg_val &= ETS_RST;
27
28 /* ETS Algorith */
29 switch (etsalg & SXGBE_MTL_OPMODE_ESTMASK) {

Logically dead code (DEADCODE)

30 case ETS_WRR:
31 reg_val &= ETS_WRR;
32 break;


Logically dead code (DEADCODE)

33 case ETS_WFQ:
34 reg_val |= ETS_WFQ;
35 break;

Logically dead code (DEADCODE)

36 case ETS_DWRR:
37 reg_val |= ETS_DWRR;
38 break;
39 }

SXGBE_MTL_OPMODE_ESTMASK is defined as 0x03
ETS_WRR is 0xFFFFFF9F
ETS_WFQ is 0x00000020
ETS_DWRR is 0x00000040

so the masking of etsalg & SXGBE_MTL_OPMODE_ESTMASK will never match any
of the ETS_* values, hence the dead code.


40 writel(reg_val, ioaddr + SXGBE_MTL_OP_MODE_REG);
41
42 switch (raa & SXGBE_MTL_OPMODE_RAAMASK) {

Logically dead code (DEADCODE)

43 case RAA_SP:
44 reg_val &= RAA_SP;
45 break;

Logically dead code (DEADCODE)

46 case RAA_WSP:
47 reg_val |= RAA_WSP;
48 break;
49 }
50 writel(reg_val, ioaddr + SXGBE_MTL_OP_MODE_REG);
51}

SXGBE_MTL_OPMODE_RAAMASK is defined as 0x1
RAA_SP is 0xFFFFFFFB
RAA_WSP is 0x00000004

so masking of raa & SXGBE_MTL_OPMODE_RAAMASK will never match any of the
RAA_* values, hence the dead code.

I don't think this is intentional. Not sure how to fix this hence I'm
reporting this issue.

Regards,

Colin