[U-Boot] [PATCH V2 3/3] sunxi: Fix A33 memory initialization

[Philipp Tomsich]

Dipl.-Ing. Dr.techn. Philipp Tomsich
Theobroma Systems Design und Consulting GmbH
Seestadtstrasse 27 (Aspern IQ), A-1220 Wien, Austria
Phone: +43 1 2369893-401, Fax: +43 1 2369893-9-401
Cell phone: +43 664 8346109
http://www.theobroma-systems.com <http://www.theobroma-systems.com/>




> On 15.02.2019, at 12:31, Andre Przywara <andre.przywara at arm.com> wrote:
> 
> On Fri, 15 Feb 2019 11:18:38 +0100
> Philipp Tomsich <philipp.tomsich at theobroma-systems.com> wrote:
> 
> Hi Philipp,
> 
>>> On 14.02.2019, at 22:24, André Przywara <andre.przywara at arm.com> wrote:
>>> 
>>> On 14/02/2019 16:36, Philipp Tomsich wrote:  
>>>> 
>>>> 
>>>>> On 14.02.2019, at 16:58, Michael Trimarchi <michael at amarulasolutions.com> wrote:
>>>>> 
>>>>> Set two rank timing and exit self-refresh timing seems not done
>>>>> properly. We know use the same write that we are using
>>>>> on H5 silicon. Tested was done in A33 allwinner cpu, dual rank
>>>>> connection connected with two MT41K512M16HA-125:A memory model.
>>>>> Memory is configure as DDR3 1.5V
>>>>> 
>>>>> Signed-off-by: Michael Trimarchi <michael at amarulasolutions.com>
>>>>> ---
>>>>> 
>>>>> V1->V2: adjust commit message
>>>>> 
>>>>> ---
>>>>> arch/arm/mach-sunxi/dram_sun8i_a33.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>> 
>>>>> diff --git a/arch/arm/mach-sunxi/dram_sun8i_a33.c b/arch/arm/mach-sunxi/dram_sun8i_a33.c
>>>>> index d73a93a132..355fe30aba 100644
>>>>> --- a/arch/arm/mach-sunxi/dram_sun8i_a33.c
>>>>> +++ b/arch/arm/mach-sunxi/dram_sun8i_a33.c
>>>>> @@ -146,7 +146,7 @@ static void auto_set_timing_para(struct dram_para *para)
>>>>> 	writel(reg_val, &mctl_ctl->dramtmg5);
>>>>> 	/* Set two rank timing and exit self-refresh timing */
>>>>> 	clrsetbits_le32(&mctl_ctl->dramtmg8, (0xff << 8) | (0xff << 0),
>>>>> -			0x33 << 8 | (0x8 << 0));
>>>>> +			0x33 << 8 | (0x10 << 0));  
>>>> 
>>>> How exactly does the change in constants match up with the commit message?
>>>> What is the field at “<< 0”?  
>>> 
>>> From looking at the ZynqMP register guide, which is reported to be close
>>> to the various Allwinner DRAM controllers, bits [6:0] are tXS: Self
>>> refresh exit delay. Increasing that should not hurt, and if I understand
>>> it correctly it only affects the time after the self-refresh *exit*,
>>> which happens only after (re-)initialisation(?).  
>> 
>> The “set two rank timing” comment doesn’t match our expectation that
>> this will be self-refresh timings, as on the ZynqMP or the A80.
>> Self-refresh only happens, if someone puts the DRAM into self-refresh
>> (i.e. “suspend to DRAM”) and then resumes it.  I don’t see a reference
>> to the error occurring from this.
> 
> So I was wondering about this as well. Indeed we don't seem to *explicitly* enter or exit Self-Refresh anywhere, but maybe this is done implicitly as part of some training phase?
> I might be wrong about this, but in some DDR3 documentation I see that changing the DLL state is connected to self refresh, and enabling the DLL is required as part of the initialisation? So is the DRAMC somehow triggering a self refresh exit "magically"? If I understand this correctly, our ranking test does reset the controller?

I’d need to reread JESD79 (a much more relaxing read than the daily news),
to figure out whether there’s any valid reason to play with self-refresh during
the training.

>> That said, if the field indeed was the exit self-refresh timing, this would
>> usually be tXSDLL, encoded as tXSDLL/32. JESD79 specifies tESXR as
>> tXSDLL (which in turn is tDLLK(min)), which is 512 nCK always: 0x10
>> would be 512 and 0x08 would only be 256… then again, this should only
>> matter when exiting self-refresh.
> 
> So I was looking at this:
> https://www.xilinx.com/html_docs/registers/ug1087/ddrc___dramtmg8.html
> and tXSDLL is bits [14:8], while the non-DLL tXS is bits [6:0].
> 
>> Note that the ‘auto-enter self-refresh’ functionality is controlled through
>> BIT(3) in PWRCTL on the A33, according to Allwinner’s basic_loader.
>> I don’t know whether that may be turned on by the driver (i.e. didn’t
>> check).
> 
> I don't see us touching pwrctl for the A33 (but for the A23).
> 
>> OTOH, when working with an underdocumented DRAM register layout
>> and once one has an educated guess at what register/setting may be
>> affected, a DRAM protocol analyzer can provide conclusive answers
>> by looking at the differences in behaviour with 0x8 and 0x10 in that
>> bitfield…
> 
> All I have is a multimeter and no A33 ;-)

You are aware that was more of a philosophical rambling and not intended
as a request to you…
However, I am way more surprised that none of the parties having money
riding on their A33 designs has gone through the required effort.

Cheers,
Philipp.