[PATCH] mtd: rawnand: brcmnand: Fix data access violation for STB chip

[Florian Fainelli]

On 3/20/2024 3:26 PM, William Zhang wrote:
> Florian reported the following kernel NULL pointer dereference issue on
> a BCM7250 board:
> [    2.829744] Unable to handle kernel NULL pointer dereference at virtual address 0000000c when read
> [    2.838740] [0000000c] *pgd=80000000004003, *pmd=00000000
> [    2.844178] Internal error: Oops: 206 [#1] SMP ARM
> [    2.848990] Modules linked in:
> [    2.852061] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.8.0-next-20240305-gd95fcdf4961d #66
> [    2.860436] Hardware name: Broadcom STB (Flattened Device Tree)
> [    2.866371] PC is at brcmnand_read_by_pio+0x180/0x278
> [    2.871449] LR is at __wait_for_common+0x9c/0x1b0
> [    2.876178] pc : [<c094b6cc>]    lr : [<c0e66310>]    psr: 60000053
> [    2.882460] sp : f0811a80  ip : 00000012  fp : 00000000
> [    2.887699] r10: 00000000  r9 : 00000000  r8 : c3790000
> [    2.892936] r7 : 00000000  r6 : 00000000  r5 : c35db440  r4 : ffe00000
> [    2.899479] r3 : f15cb814  r2 : 00000000  r1 : 00000000  r0 : 00000000
> 
> The issue only happens when dma mode is disabled or not supported on STB
> chip. The pio mode transfer calls brcmnand_read_data_bus function which
> dereferences ctrl->soc->read_data_bus. But the soc member in STB chip is
> NULL hence triggers the access violation. The function needs to check
> the soc pointer first.
> 
> Fixes: 546e42599120 ("mtd: rawnand: brcmnand: Add BCMBCA read data bus interface")
> 
> Reported-by: Florian Fainelli <florian.fainelli at broadcom.com>
> Tested-by: Florian Fainelli <florian.fainelli at broadcom.com>
> Signed-off-by: William Zhang <william.zhang at broadcom.com>

Thanks for the quick fix William, I had missed that the difference 
between systems was indeed FLASH_DMA being enabled or not.
-- 
Florian