Coverity: nxp_spifi_write_reg(): Integer handling issues

Hello!

This is an experimental automated report about issues detected by Coverity from a scan of next-20200410 as part of the linux-next weekly scan project:
https://scan.coverity.com/projects/linux-next-weekly-scan

You're getting this email because you were associated with the identified lines of code (noted below) that were touched by recent commits:

f617b9587c16 ("mtd: spi-nor: add driver for NXP SPI Flash Interface (SPIFI)")

Coverity reported the following:

*** CID 1324209: Integer handling issues (SIGN_EXTENSION) /drivers/mtd/spi-nor/controllers/nxp-spifi.c: 162 in nxp_spifi_write_reg()

156     	ret = nxp_spifi_set_memory_mode_off(spifi);
157     	if (ret)
158     		return ret;
159
160     	cmd = SPIFI_CMD_DOUT |
161     	      SPIFI_CMD_DATALEN(len) |
vvv     CID 1324209:  Integer handling issues  (SIGN_EXTENSION)
vvv     Suspicious implicit sign extension: "opcode" with type "u8" (8 bits, unsigned) is promoted in "opcode << 24" to type "int" (32 bits, signed), then sign-extended to type "unsigned long" (64 bits, unsigned).  If "opcode << 24" is greater than 0x7FFFFFFF, the upper bits of the result will all be 1.
162     	      SPIFI_CMD_OPCODE(opcode) |
163     	      SPIFI_CMD_FIELDFORM_ALL_SERIAL |
164     	      SPIFI_CMD_FRAMEFORM_OPCODE_ONLY;
165     	writel(cmd, spifi->io_base + SPIFI_CMD);

166
167 while (len--)

If this is a false positive, please let us know so we can mark it as such, or teach the Coverity rules to be smarter. If not, please make sure fixes get into linux-next. :) For patches fixing this, please include these lines (but double-check the "Fixes" first):

Addresses-Coverity-ID: 1324209 ("Integer handling issues")

Human edit: this issue is also repeated again at
drivers/mtd/spi-nor/controllers/nxp-spifi.c: 205
and
drivers/mtd/spi-nor/controllers/nxp-spifi.c: 138

Thanks for your attention!

Coverity-bot

This commit is from 2015. I see now that this might have gotten re-identified due to a file naming?

a0900d0195d2 ("mtd: spi-nor: Prepare core / manufacturer code split")

-Kees

Kees Cook