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Date:   Mon, 2 Apr 2018 22:20:20 +0200
From:   Boris Brezillon <boris.brezillon@bootlin.com>
To:     Peter Rosin <peda@axentia.se>
Cc:     Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Josh Wu <rainyfeeling@outlook.com>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        linux-kernel@vger.kernel.org, Marek Vasut <marek.vasut@gmail.com>,
        linux-mtd@lists.infradead.org,
        Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
        Brian Norris <computersforpeace@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using
 dma
Message-ID: <20180402222020.1d344c14@bbrezillon>
In-Reply-To: <20180402212843.164d5d21@bbrezillon>
References: <20180329131054.22506-1-peda@axentia.se>
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        <ed87cf13-a69a-6115-f0a8-5f51c4957d1d@axentia.se>
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        <b740406a-e91c-67ad-24a3-cbdbe259d00d@axentia.se>
        <20180402142249.7e076a64@bbrezillon>
        <e0d9bd59-8031-e387-676e-dc5811170a0c@axentia.se>
        <20180402212843.164d5d21@bbrezillon>
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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.

Can you try to write 0x3 to 0xFFFFECCC and 0x30 to 0xFFFFECD4?

> 
> > 
> > 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
> >   
> 
> [1]https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c#L498
> 


-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com