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Date:   Mon, 8 Aug 2022 10:54:37 +0200
From:   Marco Felsch <m.felsch@pengutronix.de>
To:     Adam Ford <aford173@gmail.com>
Cc:     Biju Das <biju.das.jz@bp.renesas.com>,
        Dave Stevenson <dave.stevenson@raspberrypi.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        David Airlie <airlied@linux.ie>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Marek Vasut <marex@denx.de>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Jagan Teki <jagan@amarulasolutions.com>,
        "robert.chiras@nxp.com" <robert.chiras@nxp.com>,
        "laurentiu.palcu@nxp.com" <laurentiu.palcu@nxp.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Jonas Karlman <jonas@kwiboo.se>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        arm-soc <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Robert Foss <robert.foss@linaro.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>
Subject: Re: imx8mm lcdif->dsi->adv7535 no video, no errors
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On 22-08-07, Adam Ford wrote:
> On Fri, Aug 5, 2022 at 4:05 PM Adam Ford <aford173@gmail.com> wrote:
> >
> > On Fri, Aug 5, 2022 at 7:56 AM Adam Ford <aford173@gmail.com> wrote:
> > >
> > > On Fri, Aug 5, 2022 at 5:55 AM Adam Ford <aford173@gmail.com> wrote:
> > > >
> > > > On Fri, Aug 5, 2022 at 3:44 AM Biju Das <biju.das.jz@bp.renesas.com> wrote:
> > > > >
> > > > > Hi Adam and all,
> > > > >
> > > > > > Subject: Re: imx8mm lcdif->dsi->adv7535 no video, no errors
> > > > > >
> > > > > > On Thu, Aug 4, 2022 at 9:52 AM Dave Stevenson
> > > > > > <dave.stevenson@raspberrypi.com> wrote:
> > > > > > >
> > > > > > > On Thu, 4 Aug 2022 at 13:51, Marco Felsch <m.felsch@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@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@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@60 on 4
> > > > > > > lanes is again listed as mandatory for using the timing generator).
> > >
> > > Marco,
> > >
> > > Looking through the DSIM driver that NXP uses, it appears that they
> > > have a few special cases where they intentionally manipulate the DSIM
> > > under certain conditions:
> > >
> > > /* '1280x720@60Hz' mode with 2 data lanes
> > > * requires special fine tuning for DPHY
> > > * TIMING config according to the tests.
> > > */
> > >
> > > There is also a separate one for the 4-lane mode:
> > >
> > > /* workaround for CEA standard mode "1280x720@60" "1920x1080p24"
> > > * display on 4 data lanes with Non-burst with sync
> > > * pulse DSI mode, since use the standard horizontal
> > > * timings cannot display correctly. And this code
> > > * cannot be put into the dsim Bridge's mode_fixup,
> > > * since the DSI device lane number change always
> > > * happens after that.
> > > */
> > >
> > > And lastly, they address issues with 3-lane mode:
> > >
> > > /* TODO: DSIM 3 lanes has some display issue, so
> > > * avoid 3 lanes enable, and force data lanes to
> > > * be 2.
> > > */
> > >
> > > Since the ADV is trying to adjust the lanes to 3 when running at 720p,
> > > it could be part of the reason you need to jump to 2-lane mode.
> > >
> > > > > > >
> > > > > > > > > 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 tested running various modes with the timing generator disable on an
> > NXP kernel with functional video, and some of the video modes stopped
> > operating or became blurry.  With the generator on, it appeared to
> > make the issues go away, so I think it should be left on.
> >
> > > > > > >
> > > > > > > > > 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.
> > > > >
> > > > > Does it mean theoretically rescale of lanes is not required??
> > > >
> > > > On the custom kernel from NXP, I can sync at 720p at 4-lanes.
> > > > Unfortunately, I haven't yet been able to replicate all the register
> > > > settings between my working version at 720p and my non-working
> > > > version, and I still have yet to sync at 720p using the mainline
> > > > adv7535 driver.  I am still wrokong on it.
> > > >
> > > > > At least 2 platforms can work with fixed 4 lanes@720p.
> > >
> > > Based on what I'm seeing for this NXP platform, it almost seems like
> > > the DSI transmitter should make the determination on whether or not to
> > > scale the number of lanes instead of having the ADV7373 do it.  Since
> > > their custom kernel is able to do 720p in 4-lane mode with this part,
> > > it doesn't seem unreasonable to me.
> >
> > I did a bunch of comparisons between registers for both the ADV7535
> > and the DSIM, and it appears that the video information is somehow
> > different between the working NXP kernel and non-working one.
> >
> > The two main differences are around the values of htotal  hfp.  Both
> > the DSIM and the ADV7535 are using different values for htotal and the
> > hfp between the kernels.  I am wondering if there is a bug in the 5.19
> > driver which is fetching wrong info or somehow the data isn't being
> > calculated properly because both the DSIM and the ADV timings match
> > each other, but don't match the working kernel.
> >
> >
> > 720p Working on NXP:
> >
> > [   24.657957] sec_mipi_dsim_set_main_mode: vmode->hfront_porch 112 ->
> > hfp_wc = 78
> > [   24.665284] sec_mipi_dsim_set_main_mode: vmode->hsync_len 40 -> hsa_wc = 24
> > [   24.681496] adv7511_dsi_config_timing_gen: htotal 1652
> > [   24.691372] adv7511_dsi_config_timing_gen: hfp 112
> >
> > 720p Not working:
> >
> > [  106.424404] samsung_dsim_set_display_mode: vfp = 5
> > [  106.429216] samsung_dsim_set_display_mode: bfp = 20
> > [  106.441777] sec_mipi_dsim_set_main_mode: vmode->hfront_porch 110 ->
> > hfp_wc = 77
> > [  106.449221] sec_mipi_dsim_set_main_mode: vmode->hsync_len 40 -> hsa_wc = 24
> > [  106.456314] LCD size = 1280x720
> > [  106.470115] adv7511_dsi_config_timing_gen: htotal = 1650
> > [  106.480707] adv7511_dsi_config_timing_gen: hfp = 110
> >
> 
> After spending more time than I care to admit, I think I have a
> working solution to the DSIM + ADV7535, but the vast majority of the
> changes I had to do were revolving around samsung_dsim_set_phy_ctrl.
> I have an LVDS bridge based on the ti,sn65dsi83.  With some
> suggestions from Marek V, I replaced the fixed-clock solution with a
> dynamic one based on the attached bridge's requested clocks.
> 
> With those changes, I have the following resolutions working on the
> ADV7535 (with almost no chages to the ADV code) ane one that's nearly
> working:
> 
> Working:
> 
> 1080p@60
> 1080p@50
> 720p@50
> 800x600-75
> 720x576
> 
> Partially Working:
> 720p@60 (hsync appears off, rounding error?)
> 
> This driver appears to be using a fixed frequency and the
> corresponding fixed frequency in the DPHY settings. If the clock
> changes, the samsung_dsim_set_phy_ctrl needs to adjust accordingly.
> NXP lists a 2-lane operation mode for 720 as needing some additional
> adjustments because the calculations don't quite line up, but due to
> the other changes I made, I didn't investigate 2-lane very much.
> 
> In order to switch resolutions, I had to lock the adv7535 in 4-lane
> mode with a minor patch to the adv driver, because the DSIM doesn't
> appear to operate in 3-lane mode (like the adv7511 wants to do) and
> the DSIM seemed to be unhappy about the connections and
> disconnections.  I also made some changes to the PMS calibration for
> the PLL which allowed me to lower the phy clock a bit.
> 
> The rest of the changes I did were attempting to port the dsim dphy
> frequency tables from NXP's kernel.  If anyone from NXP or Samsung has
> the formula for how to determine some of the values for the DPHY, I'd
> like to replace the look-up table [1] with a formula.
> 
> Once I have my code changes cleaned up, I'll push them to a github and
> share the info.
> 
> [1] - https://source.codeaurora.org/external/imx/linux-imx/tree/include/drm/bridge/sec_mipi_dsim.h?h=lf-5.15.y

Hi Adam,

thanks for your work and sharing. Did you tested our current solution
since we think that we understood the DSIM porches? As I said in the
very beginning of this discussion, NXP took some porch values we really
don't understand and I don't think they do either. NXP tweaked the
values somehow so the chip is producing at least the most wanted
resolutions.

Regards,
  Marco