Date:   Tue, 3 Apr 2018 08:51:10 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Josh Wu <rainyfeeling@...look.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using
 dma

On 2018-04-02 22:20, Boris Brezillon wrote:
> On Mon, 2 Apr 2018 21:28:43 +0200
> Boris Brezillon <boris.brezillon@...tlin.com> wrote:
> 
>> On Mon, 2 Apr 2018 19:59:39 +0200
>> Peter Rosin <peda@...ntia.se> wrote:
>>
>>> On 2018-04-02 14:22, Boris Brezillon wrote:  
>>>> On Thu, 29 Mar 2018 16:27:12 +0200
>>>> Peter Rosin <peda@...ntia.se> wrote:
>>>>     
>>>>> On 2018-03-29 15:44, Boris Brezillon wrote:    
>>>>>> On Thu, 29 Mar 2018 15:37:43 +0200
>>>>>> Peter Rosin <peda@...ntia.se> wrote:
>>>>>>       
>>>>>>> On 2018-03-29 15:33, Boris Brezillon wrote:      
>>>>>>>> On Thu, 29 Mar 2018 15:10:54 +0200
>>>>>>>> Peter Rosin <peda@...ntia.se> 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@...ntia.se>
>>>>>>>>> ---
>>>>>>>>>  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.  
>>
>> Ok.
>>
>>>   
>>>>> 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.  
>>
>> I don't use devmem2. Is 'readback' information accurate or is it
>> always what's been written? Because when you write 0x33 to 0xFFFFECBC,
>> 0x33 is read back, but just after that, when you read it again it's 0.
>>
>>> BTW, how do I
>>> know which master is in use for the LCD controller? 8 or 9? Both?  
>>
>> It's configurable on a per-layer basis through the SIF bit in
>> LCDC_<layer>CFG0. The driver tries to dispatch the load on those 2 AHB
>> masters [1].
>>
>>> And
>>> which DDR slave is the target? 7, 8, 9 or 10? More than one?  
>>
>> This, I don't know. I guess all of them can be used.
> 
> Looks like I was wrong. According to "Table 15-3. SAMA5D3 Master to
> Slave Access", LCDC port 0 can only access DDR port 2 and LCDC port 1
> can only access DDR port 3.
> 
> Can you try to write 0x3 to 0xFFFFECCC and 0x30 to 0xFFFFECD4?

Given the matrix dump in the other mail, it is not surprising that I
can't. But if I change the matrix from the default

 0 33--3--3--3333--
 1 33--3--3--3333--
 2 33--------------
 3 -3--------333---
 4 33--------------
 5 3---------------
 6 33--33-33333333-
 7 --3-3--3--------
 8 -3---3--3--3----
 9 --3-3--3-33-333-
10 3--3------------
11 3-----3---------
12 ----------------
13 ----------------
14 ----------------
15 ----------------

to

 0 33--3--3--3333--
 1 33--3--3--3333--
 2 33--------------
 3 -3--------333---
 4 33--------------
 5 3---------------
 6 33--33-33333333-
 7 --1-1--3--------
 8 -1---1--3--3----
 9 --1-1--3-33-333-
10 3--3------------
11 3-----3---------
12 ----------------
13 ----------------
14 ----------------
15 ----------------

which I *think* is reducing the prio of accesses from all DMAC masters
to all DDR slaves, and then change the ULBT to 1 (SINGLE) for all
six DMAC masters, I still get the same display disturbances on nand
accesses. And I can't seem to tweak the LQOSENx bits, at least not for
the DMAC/DDR case.

Cheers,
Peter

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