On 2018-03-29 16:27, Peter Rosin wrote:

On 2018-03-29 15:44, Boris Brezillon wrote:

quoted

On Thu, 29 Mar 2018 15:37:43 +0200
Peter Rosin [off-list ref] wrote:

quoted

On 2018-03-29 15:33, Boris Brezillon wrote:

quoted

On Thu, 29 Mar 2018 15:10:54 +0200
Peter Rosin [off-list ref] wrote:
  

quoted

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 <redacted>
---
 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. But when I try to write to "Priority Registers B For Slaves" it doesn't
take, regardless of write protect mode.

Can the relevant bits only be written when the HLCDC is inactive or
something?

Here is someone else with what seems like very similar problems[1], however
also with USB disturbing the display. I can't test that (easily) since a
mux in front of the USB port was unfortunately wired incorrectly in this
first attempt. And USB disturbing the display is not a showstopper around
here, since USB will only be used for debugging etc in my case.

[1] https://www.avrfreaks.net/forum/sama5d31-ahb-bus-matrix-lcd

Cheers,
Peter