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

[Peter Rosin <peda@axentia.se>]

Hi Nicolas,

Boris asked for your input on this (the datasheet difference appears to
have no bearing on the issue) elsewhere in the tree of messages. It's
now been a week or so and I'm starting to wonder if you missed this
altogether or if you are simply out of office or something?

Cheers,
Peter

On 2018-04-03 09:18, Boris Brezillon wrote:
> On Tue, 3 Apr 2018 08:11:30 +0200
> Peter Rosin <peda@axentia.se> wrote:
> 
>> On 2018-04-02 22:20, Boris Brezillon wrote:
>>> On Mon, 2 Apr 2018 21:28:43 +0200
>>> Boris Brezillon <boris.brezillon@bootlin.com> wrote:
>>>   
>>>> On Mon, 2 Apr 2018 19:59:39 +0200
>>>> Peter Rosin <peda@axentia.se> wrote:
>>>>  
>>>>> On 2018-04-02 14:22, Boris Brezillon wrote:    
>>>>>> On Thu, 29 Mar 2018 16:27:12 +0200
>>>>>> Peter Rosin <peda@axentia.se> wrote:
>>>>>>       
>>>>>>> On 2018-03-29 15:44, Boris Brezillon wrote:      
>>>>>>>> On Thu, 29 Mar 2018 15:37:43 +0200
>>>>>>>> Peter Rosin <peda@axentia.se> wrote:
>>>>>>>>         
>>>>>>>>> On 2018-03-29 15:33, Boris Brezillon wrote:        
>>>>>>>>>> On Thu, 29 Mar 2018 15:10:54 +0200
>>>>>>>>>> Peter Rosin <peda@axentia.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@axentia.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.  
>>
>> About that table, someone with HW-knowledge should have a real close
>> look at it! Why?
>>
>> I peeked at all the PRxSy registers and there are a lot of '3' entries
>> for all the MxPR fields. In fact, the '3' entries align very neatly
>> with the checks in this "Master to Slave Access" table. Except they
>> don't, after a while.
>>
>> Here's how the table looks in my datasheet:
>>
>>  0 vv--v--v--vvvv-
>>  1 vv--v--v--vvvv-
>>  2 vv-------------
>>  3 vv--------vvv--
>>  4 vv-------------
>>  5 v--------------
>>  6 vv--vv-vvvvvvvv
>>    v--------------
>>  7 v--------------
>>  8 --v-v--v-------
>>  9 -v---v--v--v---
>> 10 ---------vv-vvv
>> 11 v--v-----------
>> 12 v-----v--------
>>
>> And here's the '3' entries when digging in the registers (the extra
>> dash at the end is for the 16th non-existent slave):
>>
>>  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 ----------------
>>
>> There's a big mismatch for the four DDR2 lines in the table; they
>> seem to map to only three registers. Other than that, the only tweak
>> or anomaly is that first entry (Cortex A5) for master 3 (Int ROM).
>>
>> *time passes*
>>
>> Arrrgh!! You say "Table 15-3". This is Table 14-3 for me! I believe
>> I'm using the latest datasheet (02-Feb-16). What are you reading???!?
> 
> Oops, I was reading an old datasheet (from 2014).