mfd: lpc_ich: Do not touch SPI-NOR write protection bit on Haswell/Broadwell

At least on Lenovo Thinkpad Yoga, the BIOS seems to monitor the SPI-NOR
write protection bit and if it is flipped to read/write it assumes the
BIOS configuration was changed on next reboot. It then, for unknown
reasons, resets the BIOS settings back to default.

We can prevent this by just leaving the write protection bit intact and
let the SPI-NOR driver know whether the device is writable or not. In
case of this particular Lenovo the SPI-NOR flash will be exposed as
read-only.

Fixes: ff00d7a3 ("mfd: lpc_ich: Add support for SPI serial flash host controller")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=195951Reported-by: Abdó Roig-Marange <abdo.roig@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/lpc_ich.c

@@ -1119,17 +1119,7 @@ static int lpc_ich_init_spi(struct pci_dev *dev)
 			res->start = spi_base + SPIBASE_LPT;
 			res->end = res->start + SPIBASE_LPT_SZ - 1;
 
-			/*
-			 * Try to make the flash chip writeable now by
-			 * setting BCR_WPD. It it fails we tell the driver
-			 * that it can only read the chip.
-			 */
 			pci_read_config_dword(dev, BCR, &bcr);
-			if (!(bcr & BCR_WPD)) {
-				bcr |= BCR_WPD;
-				pci_write_config_dword(dev, BCR, bcr);
-				pci_read_config_dword(dev, BCR, &bcr);
-			}
 			info->writeable = !!(bcr & BCR_WPD);
 		}
 		break;