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SubjectRe: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma
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).

> Is that something that adds to the confusion?
>
> > Can you try to write 0x3 to 0xFFFFECCC and 0x30 to 0xFFFFECD4?
>
> Will continue experimenting...
>
> Cheers,
> Peter



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

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