Re: [PATCH] arm64: dts: imx8mp: Add TC9595 bridge on DH electronics i.MX8M Plus DHCOM

From: Alexander Stein <alexander.stein@ew.tq-group.com>
To: Marek Vasut <marex@denx.de>
Cc: linux-arm-kernel@lists.infradead.org,
	Conor Dooley <conor+dt@kernel.org>,
	Fabio Estevam <festevam@gmail.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Rob Herring <robh+dt@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Shawn Guo <shawnguo@kernel.org>,
	devicetree@vger.kernel.org
Subject: Re: [PATCH] arm64: dts: imx8mp: Add TC9595 bridge on DH electronics i.MX8M Plus DHCOM
Date: Wed, 24 May 2023 08:49:04 +0200	[thread overview]
Message-ID: <3741758.kQq0lBPeGt@steina-w> (raw)
In-Reply-To: <43cb9c13-7d65-064e-943c-a9d3e6c63f64@denx.de>

Hi Marek,

Am Dienstag, 23. Mai 2023, 15:10:05 CEST schrieb Marek Vasut:
> On 5/23/23 13:17, Alexander Stein wrote:
> > Hello Marek,
> 
> Hi,
> 
> > Am Montag, 15. Mai 2023, 18:24:24 CEST schrieb Marek Vasut:
> >> Add TC9595 DSI-to-DPI and DSI-to-(e)DP bridge to
> >> DH electronics i.MX8M Plus DHCOM SoM . The bridge
> >> is populated on the SoM, but disabled by default
> >> unless used for display output.
> >> 
> >> Signed-off-by: Marek Vasut <marex@denx.de>
> > 
> > Were you actually able to access the display? E.g. reading DPCD via AUX
> > channel?
> 
> I only tried the full display port (the one with large plug) on the TC
> evaluation kit, there I could use the aux channel. Are you testing this
> bridge and running into issues ? Details please ?

Which SoC is this evaluation kit based on?
Yes, I'm trying to test this bridge on imx8mp based board. 

AFAICS I run into a timeout during drm connector .get_modes call, see kernel 
log below.

> samsung-dsim 32e60000.dsi: [drm:samsung_dsim_host_attach [samsung_dsim]] 
Attached tc358767 device
> tc358767 1-000f: failed to read DPCD: -110
> tc358767 1-000f: failed to read display props: -110

Looking at the AUX_CH+/- signals, I can see the native aux request and the 
(presumable) correct answer (DP_DPCD_REV register) from the display. But for 
some reason the bridge runs into a aux timeout.
I can see in the DP0_AUXSTATUS register the bus gets busy (0x1) after starting 
transfer. But after the tc_aux_wait_busy() call DP0_AUXSTATUS his indicating a 
timeout and sync error (0x310002).
When changing the "Aux Bit Period Calculator Threshold" to 5 (register 
AUXCFG1), the sync error is gone, but the timeout still happens.

The frequency used from the display is ~1MHz, which should be okay. So on the 
electrical side all seems okay, but the native aux transfer don't work.

Any ideas?

Best regards,
Alexander
-- 
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Amtsgericht München, HRB 105018
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