Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma

[Peter Rosin]

On 2018-04-02 14:22, Boris Brezillon wrote:
> On Thu, 29 Mar 2018 16:27:12 +0200
> Peter Rosin <peda@xxxxxxxxxx> wrote:
> 
>> On 2018-03-29 15:44, Boris Brezillon wrote:
>>> On Thu, 29 Mar 2018 15:37:43 +0200
>>> Peter Rosin <peda@xxxxxxxxxx> wrote:
>>>   
>>>> On 2018-03-29 15:33, Boris Brezillon wrote:  
>>>>> On Thu, 29 Mar 2018 15:10:54 +0200
>>>>> Peter Rosin <peda@xxxxxxxxxx> wrote:
>>>>>     
>>>>>> On a sama5d31 with a Full-HD dual LVDS panel (132MHz pixel clock) NAND
>>>>>> flash accesses have a tendency to cause display disturbances. Add a
>>>>>> module param to disable DMA from the NAND controller, since that fixes
>>>>>> the display problem for me.
>>>>>>
>>>>>> Signed-off-by: Peter Rosin <peda@xxxxxxxxxx>
>>>>>> ---
>>>>>>  drivers/mtd/nand/raw/atmel/nand-controller.c | 7 ++++++-
>>>>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c b/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>>>> index b2f00b398490..2ff7a77c7b8e 100644
>>>>>> --- a/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>>>> +++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>>>> @@ -129,6 +129,11 @@
>>>>>>  #define DEFAULT_TIMEOUT_MS			1000
>>>>>>  #define MIN_DMA_LEN				128
>>>>>>  
>>>>>> +static bool atmel_nand_avoid_dma __read_mostly;
>>>>>> +
>>>>>> +MODULE_PARM_DESC(avoiddma, "Avoid using DMA");
>>>>>> +module_param_named(avoiddma, atmel_nand_avoid_dma, bool, 0400);    
>>>>>
>>>>> I'm not a big fan of those driver specific cmdline parameters. Can't we
>>>>> instead give an higher priority to HLCDC master using the bus matrix?    
>>>>
>>>> I don't know if it will be enough, but we sure can try. However, I have
>>>> no idea how to do that. I will happily test stuff though...  
>>>
>>> There's no interface to configure that from Linux, but you can try to
>>> tweak it with devmem and if that does the trick, maybe we can expose a
>>> way to configure that from Linux. For more details, see the "Bus Matrix
>>> (MATRIX)" section in Atmel datasheets.  
>>
>> I don't seem to succeed in changing the registers I think I need to change.
>> I can poke the "Write Protection Mode Register" by writing MAT0 and MAT1 to
>> it.
> 
> You mean 0x4D415400, right? ("MAT0" != 0x4D415400).

Bits 1 through 7 do not matter, so even though not equal they are (or
should be) equivalent. But I did use 0x4d415400. I simply used the
shorter syntax since that was easier to type and conveyed the relevant
info.

>> But when I try to write to "Priority Registers B For Slaves" it doesn't
>> take, regardless of write protect mode.
> 
> Did you check MATRIX_WPSR after writing to MATRIX_PRXSY?

No, but did it again and checked, see transcript below. BTW, how do I
know which master is in use for the LCD controller? 8 or 9? Both? And
which DDR slave is the target? 7, 8, 9 or 10? More than one?

Cheers,
Peter

# devmem2 0xffffede4 w
/dev/mem opened.
Memory mapped at address 0xb6f50000.
Value at address 0xFFFFEDE4 (0xb6f50de4): 0x0
# devmem2 0xffffede4 w 0x4d415401
/dev/mem opened.
Memory mapped at address 0xb6f0d000.
Value at address 0xFFFFEDE4 (0xb6f0dde4): 0x0
Written 0x4D415401; readback 0x4D415401
# devmem2 0xffffede4 w
/dev/mem opened.
Memory mapped at address 0xb6f55000.
Value at address 0xFFFFEDE4 (0xb6f55de4): 0x1
# devmem2 0xffffede4 w 0x4d415400
/dev/mem opened.
Memory mapped at address 0xb6fb5000.
Value at address 0xFFFFEDE4 (0xb6fb5de4): 0x1
Written 0x4D415400; readback 0x4D415400
# devmem2 0xffffede4 w
/dev/mem opened.
Memory mapped at address 0xb6fef000.
Value at address 0xFFFFEDE4 (0xb6fefde4): 0x0


# devmem2 0xffffede8 w
/dev/mem opened.
Memory mapped at address 0xb6fe9000.
Value at address 0xFFFFEDE8 (0xb6fe9de8): 0x0


# devmem2 0xffffecbc w
/dev/mem opened.
Memory mapped at address 0xb6ff0000.
Value at address 0xFFFFECBC (0xb6ff0cbc): 0x0
# devmem2 0xffffecbc w 0x33
/dev/mem opened.
Memory mapped at address 0xb6f79000.
Value at address 0xFFFFECBC (0xb6f79cbc): 0x0
Written 0x33; readback 0x33
# devmem2 0xffffecbc w
/dev/mem opened.
Memory mapped at address 0xb6efe000.
Value at address 0xFFFFECBC (0xb6efecbc): 0x0


# devmem2 0xffffede8 w
/dev/mem opened.
Memory mapped at address 0xb6f9e000.
Value at address 0xFFFFEDE8 (0xb6f9ede8): 0x0