imx8mm lcdif->dsi->adv7535 no video, no errors

[Adam Ford]

On Thu, Aug 4, 2022 at 9:52 AM Dave Stevenson
<dave.stevenson at raspberrypi.com> wrote:
>
> On Thu, 4 Aug 2022 at 13:51, Marco Felsch <m.felsch at pengutronix.de> wrote:
> >
> > Hi Dave,
> >
> > On 22-08-04, Dave Stevenson wrote:
> > > Hi Marco
> > >
> > > On Thu, 4 Aug 2022 at 10:38, Marco Felsch <m.felsch at pengutronix.de> wrote:
> > > >
> > > > Hi Dave, Adam,
> > > >
> > > > On 22-08-03, Dave Stevenson wrote:
> > > > > Hi Adam
> > > > >
> > > > > On Wed, 3 Aug 2022 at 12:03, Adam Ford <aford173 at gmail.com> wrote:
> > > >
> > > > ...
> > > >
> > > > > > > Did managed to get access to the ADV7535 programming guide? This is the
> > > > > > > black box here. Let me check if I can provide you a link with our repo
> > > > > > > so you can test our current DSIM state if you want.
> > > > > >
> > > > > > I do have access to the programming guide, but it's under NDA, but
> > > > > > I'll try to answer questions if I can.
> > > > >
> > > > > Not meaning to butt in, but I have datasheets for ADV7533 and 7535
> > > > > from previously looking at these chips.
> > > >
> > > > Thanks for stepping into :)
> > > >
> > > > > Mine fairly plainly states:
> > > > > "The DSI receiver input supports DSI video mode operation only, and
> > > > > specifically, only supports nonburst mode with sync pulses".
> > > >
> > > > I've read this also, and we are working in nonburst mode with sync
> > > > pulses. I have no access to an MIPI-DSI analyzer therefore I can't
> > > > verify it.
> > > >
> > > > > Non-burst mode meaning that the DSI pixel rate MUST be the same as the
> > > > > HDMI pixel rate.
> > > >
> > > > On DSI side you don't have a pixel-clock instead there is bit-clock.
> > >
> > > You have an effective pixel clock, with a fixed conversion for the
> > > configuration.
> > >
> > > DSI bit-clock * number of lanes / bits_per_pixel = pixel rate.
> > > 891Mbit/s * 4 lanes / 24bpp = 148.5 Mpixels/s
> >
> > Okay, I just checked the bandwidth which must equal.
> >
> > > As noted elsewhere, the DSI is DDR, so the clock lane itself is only
> > > running at 891 / 2 = 445.5MHz.
> > >
> > > > > Section 6.1.1 "DSI Input Modes" of adv7533_hardware_user_s_guide is
> > > > > even more explicit about the requirement of DSI timing matching
> > > >
> > > > Is it possible to share the key points of the requirements?
> > >
> > > "Specifically the ADV7533 supports the Non-Burst Mode with syncs. This
> > > mode requires real time data generation as a pulse packet received
> > > becomes a pulse generated. Therefore this mode requires a continuous
> > > stream of data with correct video timing to avoid any visual
> > > artifacts."
> > >
> > > LP mode is supported on data lanes. Clock lane must remain in HS mode.
> > >
> > > "... the goal is to accurately convey DPI-type timing over DSI. This
> > > includes matching DPI pixel-transmission rates, and widths of timing
> > > events."
> >
> > Thanks for sharing.
> >
> > > > > The NXP kernel switching down to an hs_clk of 445.5MHz would therefore
> > > > > be correct for 720p operation.
> > > >
> > > > It should be absolute no difference if you work on 891MHz with 2 lanes
> > > > or on 445.5 MHz with 4 lanes. What must be ensured is that you need the
> > > > minimum required bandwidth which is roughly: 1280*720*24*60 = 1.327
> > > > GBps.
> > >
> > > Has someone changed the number of lanes in use? I'd missed that if so,
> > > but I'll agree that 891MHz over 2 lanes should work for 720p60.
> >
> > The ADV driver is changing it autom. but this logic is somehow odd and
> > there was already a approach to stop the driver doing this.
>
> I'd missed that bit in the driver where it appears to drop to 3 lanes
> for pixel clock < 80000 via a mipi_dsi_detach and _attach. Quirky, but
> probably the only way it can be achieved in the current framework.
>
> > To sync up: we have two problems:
> >   1) The 720P mode with static DSI host configuration isn't working
> >      without hacks.
> >   2) The DSI link frequency should changed as soon as required
> >      automatically. So we can provide all modes.
> >
> > I would concentrate on problem 1 first before moving on to the 2nd.
>
> If you change your link frequency, it may be worth trying a lower
> resolution again such as 720x480 @ 60fps on 2 lanes. (720480 at 60 on 4
> lanes is again listed as mandatory for using the timing generator).
>
> > > I have just noted that 720p59.94 at 24bpp on 4 lanes is listed as one
> > > of the modes that is mandatory to use the timing generator (reg 0x27
> > > bit 7 = 1). On 2 lanes it is not required.
> > > I don't know why it's referencing the 1000/1001 pixel clock rates and
> > > not the base one, as it's only a base clock change with the same
> > > timing (74.176MHz clock instead of 74.25MHz).
> >
> > Interesting! I would like to know how the HDMI block gets fetched by the
> > DSI block and how the timing-generator can influence this in good/bad
> > way. So that we know what DSI settings (freq, lanes) are sufficient.
> >
> > > > > If you do program the manual DSI divider register to allow a DSI pixel
> > > > > rate of 148.5MHz vs HDMI pixel rate of 74.25MHz, you'd be relying on
> > > >
> > > > There is no such DSI pixel rate to be precise, we only have a DSI bit
> > > > clock/rate.
> > > >
> > > > > the ADV753x having at least a half-line FIFO between DSI rx and HDMI
> > > > > tx to compensate for the differing data rates. I see no reference to
> > > > > such, and I'd be surprised if it was more than a half dozen pixels to
> > > > > compensate for the jitter in the cases where the internal timing
> > > > > generator is mandatory due to fractional bytes.
> > > >
> > > > This is interesting and would proofs our assumption that the device
> > > > don't have a FIFO :)
> > > >
> > > > Our assumptions (we don't have the datasheet/programming manual):
> > > >   - HDMI part is fetching 3 bytes per HDMI pixclk
> > > >   - Ratio between dsi-clk and hdmi-pixelclk must be 3 so the DSI and
> > > >     HDMI are in sync. So from bandwidth pov there are no differences
> > > >     between:
> > > >       - HDMI: 74.25 MHz * 24 Bit  = 1782.0 MBit/s
> > > >       - DSI:    891 MHz * 2 lanes = 1782.0 MBit/s (dsi-clock: 445.5 )
> > > >       - DSI:  445.5 MHz * 4 lanes = 1782.0 MBit/s (dsi-clock: 222.75)
> > > >
> > > >     But the ratio is different and therefore the faster clocking option
> > > >     let something 'overflow'.
> > >
> > > I'll agree that all looks consistent.
> > >
> > > > Anyway, but all this means that Adam should configure the
> > > > burst-clock-rate to 445.5 and set the lanes to 4. But this doesn't work
> > > > either and now we are back on my initial statement -> the driver needs
> > > > some attention.
> > >
> > > Things always need attention :-)
> >
> > ^^
> >
> > > I suspect that it's the use of the timing generator that is the issue.
> > > The programming guide does recommend using it for all modes, so that
> > > would be a sensible first step.
> >
> > But I tested it without the timing-generator too. Can you or Adam verify
> > the timing-generator diable logic?
>
> Sorry, running without the use of the timing generator is the issue.
> It is mandatory in some modes, but supported in all modes. Always
> using it should therefore avoid not using it in one of the mandatory
> modes (the list looks a little arbitrary).
>
> > > I will say that we had a number of issues getting this chip to do
> > > anything, and it generally seemed happier on 2 or 3 lanes instead of
> > > 4. Suffice to say that we abandoned trying to use it, despite some
> > > assistance from ADI.
> >
> > Even more interessting, what is your alternative to this chip?
>
> BCM2711 which supported dual HDMI natively.
> Our investigation of ADV7535 was when trying to build what became
> Pi400 using BCM2710/BCM2837 (only has a single HDMI output). Whilst I
> do have the prototype, the ADV was wired up weirdly with I2C so I
> never really got it running with Linux.

I think I have convinced myself that the DSIM is working good enough
to match that of the NXP.

I've gone through and made a list of the register differences between
a working display using NXP's kernel and
the non-working display.  I've identified a small handful of registers
on both the CEC bank of registers and main set of registers.

I noticed that the working NXP version doesn't rescale the number of
lanes based on the clock rate, and it stays fixed at 4 lanes.

That might actually explain some of the issues I am seeing on their
kernel still not syncing at low resolutions.

I'm going to try to go through the code and identify other differences
and see if I can hack this version of the ADv7535 driver to get it
into a similar working state as the NXP one (not that theirs is the
best).  With a couple of the hacks, I can get my screen to sync, but
it just displays blue, so I think I am making some progress.

I should have a few more hours tomorrow to work on this.  It's a
side-project for me, but I have time over the weekend too.

adam
>
>   Dave