platform/chrome: chromeos_pstore: Add ecc_size module parameter

On ChromiumOS devices, the `ecc_size` is set to 0 (check dmesg | grep ecc 
to see `ecc: 0`): this disables ECC for ramoops region, even when 
`ramoops.ecc=1` is given to kernel command line parameter.

Introduce `ecc_size` module parameter to provide a method to turn on ECC
for ramoops and set different values of ecc_size per devices.

A large `ecc_size` value can cause a kernel panic due to a constraint in
Reed-Solomon code library. The validation for this constraint should
belong to the common pstore RAM layer, not in each individual driver. So
this check is handled by a separate patch [1].

[1] https://lore.kernel.org/lkml/[e-mail]

Signed-off-by: Naoya Tezuka <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Tzung-Bi Shih <[e-mail]>

drivers/platform/chrome/chromeos_pstore.c

···
 #include <linux/platform_device.h>
 #include <linux/pstore_ram.h>
 
+static int ecc_size;
+module_param(ecc_size, int, 0400);
+MODULE_PARM_DESC(ecc_size, "ECC parity data size in bytes. A positive value enables ECC for the ramoops region.");
+
 static const struct dmi_system_id chromeos_pstore_dmi_table[] __initconst = {
 	{
 		/*
···
 static int __init chromeos_pstore_init(void)
 {
 	bool acpi_dev_found;
+
+	if (ecc_size > 0)
+		chromeos_ramoops_data.ecc_info.ecc_size = ecc_size;
 
 	/* First check ACPI for non-hardcoded values from firmware. */
 	acpi_dev_found = chromeos_check_acpi();