ipq40xx/ipq806x: 4.19: fix qcom-nandc panic on boot

This patch fixes the crash that occures on rawnand device.
<https://patchwork.ozlabs.org/patch/1017933/>

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/generic/hack-4.19/100-mtd-rawnand-qcom-fix-memory-corruption-that-causes-p.patch

@@ -0,0 +1,83 @@
+From c942c462411e4757aafba73bf13b5e5c7a4b62ca Mon Sep 17 00:00:00 2001
+From: Christian Lamparter <chunkeey@gmail.com>
+Date: Sun, 23 Dec 2018 00:38:55 +0100
+Subject: [PATCH] mtd: rawnand: qcom: fix memory corruption that causes panic
+
+This patch fixes a memory corruption that occured in the
+qcom-nandc driver since it was converted to nand_scan().
+
+On boot, an affected device will panic from a NPE at a weird place:
+| Unable to handle kernel NULL pointer dereference at virtual address 00000000
+| pgd = (ptrval)
+| [00000000] *pgd=00000000
+| Internal error: Oops: 80000005 [#1] SMP ARM
+| CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.9 #0
+| Hardware name: Generic DT based system
+| PC is at   (null)
+| LR is at nand_block_isbad+0x90/0xa4
+| pc : [<00000000>]    lr : [<c0592240>]    psr: 80000013
+| sp : cf839d40  ip : 00000000  fp : cfae9e20
+| r10: cf815810  r9 : 00000000  r8 : 00000000
+| r7 : 00000000  r6 : 00000000  r5 : 00000001  r4 : cf815810
+| r3 : 00000000  r2 : cfae9810  r1 : ffffffff  r0 : cf815810
+| Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
+| Control: 10c5387d  Table: 8020406a  DAC: 00000051
+| Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
+| [<c0592240>] (nand_block_isbad) from [<c0580a94>] (allocate_partition+0x7a0/0x7dc)
+| [<c0580a94>] (allocate_partition) from [<c05811e4>] (add_mtd_partitions+0x58/0x10c)
+| [<c05811e4>] (add_mtd_partitions) from [<c0581164>] (parse_mtd_partitions+0x310/0x338)
+| [<c0581164>] (parse_mtd_partitions) from [<c057def4>] (mtd_device_parse_register+0x60/0x15c)
+| [<c057def4>] (mtd_device_parse_register) from [<c059d274>] (qcom_nandc_probe+0x770/0x8f4)
+| [<c059d274>] (qcom_nandc_probe) from [<c0567f00>] (platform_drv_probe+0x34/0x70)
+
+The problem is that the nand_scan()'s qcom_nand_attach_chip callback
+is updating the nandc->max_cwperpage from 1 to 4. This causes the
+sg_init_table of clear_bam_transaction() in the driver's
+qcom_nandc_block_bad() to memset much more than what was initially
+allocated by alloc_bam_transaction().
+
+Hence, this patch restores the old behavior by performing the
+alloc_bam_transaction() after the chip was identified.
+
+Fixes: 6a3cec64f18c ("mtd: rawnand: qcom: convert driver to nand_scan()")
+Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
+---
+ drivers/mtd/nand/raw/qcom_nandc.c | 20 ++++++++++----------
+ 1 file changed, 10 insertions(+), 10 deletions(-)
+
+--- a/drivers/mtd/nand/raw/qcom_nandc.c
++++ b/drivers/mtd/nand/raw/qcom_nandc.c
+@@ -2839,6 +2839,16 @@ static int qcom_nand_host_init_and_regis
+ 	if (ret)
+ 		return ret;
+ 
++	if (nandc->props->is_bam) {
++		free_bam_transaction(nandc);
++		nandc->bam_txn = alloc_bam_transaction(nandc);
++		if (!nandc->bam_txn) {
++			dev_err(nandc->dev,
++				"failed to allocate bam transaction\n");
++			return -ENOMEM;
++		}
++	}
++
+ 	ret = mtd_device_register(mtd, NULL, 0);
+ 	if (ret)
+ 		nand_cleanup(chip);
+@@ -2853,16 +2863,6 @@ static int qcom_probe_nand_devices(struc
+ 	struct qcom_nand_host *host;
+ 	int ret;
+ 
+-	if (nandc->props->is_bam) {
+-		free_bam_transaction(nandc);
+-		nandc->bam_txn = alloc_bam_transaction(nandc);
+-		if (!nandc->bam_txn) {
+-			dev_err(nandc->dev,
+-				"failed to allocate bam transaction\n");
+-			return -ENOMEM;
+-		}
+-	}
+-
+ 	for_each_available_child_of_node(dn, child) {
+ 		host = devm_kzalloc(dev, sizeof(*host), GFP_KERNEL);
+ 		if (!host) {