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Date:   Thu, 29 Oct 2020 14:18:06 +0200
From:   Abel Vesa <abel.vesa@nxp.com>
To:     Lucas Stach <l.stach@pengutronix.de>
Cc:     Adam Ford <aford173@gmail.com>, Marek Vasut <marex@denx.de>,
        devicetree <devicetree@vger.kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Stephen Boyd <sboyd@kernel.org>,
        Fabio Estevam <festevam@gmail.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        NXP Linux Team <linux-imx@nxp.com>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Shawn Guo <shawnguo@kernel.org>,
        linux-clk <linux-clk@vger.kernel.org>,
        arm-soc <linux-arm-kernel@lists.infradead.org>
Subject: Re: [RFC 0/3] clk: imx: Implement blk-ctl driver for i.MX8MN
Message-ID: <20201029121806.exosjo6ew7jgty73@fsr-ub1664-175>
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On 20-10-29 12:54:58, Lucas Stach wrote:
> Am Montag, den 26.10.2020, 11:23 -0500 schrieb Adam Ford:
> > On Mon, Oct 26, 2020 at 10:44 AM Lucas Stach <l.stach@pengutronix.de> wrote:
> > > Am Montag, den 26.10.2020, 10:12 -0500 schrieb Adam Ford:
> > > > On Mon, Oct 26, 2020 at 9:55 AM Abel Vesa <abel.vesa@nxp.com> wrote:
> > > > > On 20-10-25 11:05:32, Adam Ford wrote:
> > > > > > On Sun, Oct 25, 2020 at 7:19 AM Marek Vasut <marex@denx.de> wrote:
> > > > > > > On 10/25/20 1:05 PM, Abel Vesa wrote:
> > > > > > > 
> > > > > > > [...]
> > > > > > > 
> > > > > > > > > Together, both the GPC and the clk-blk driver should be able to pull
> > > > > > > > > the multimedia block out of reset.  Currently, the GPC can handle the
> > > > > > > > > USB OTG and the GPU, but the LCDIF and MIPI DSI appear to be gated by
> > > > > > > > > the clock block
> > > > > > > > > 
> > > > > > > > > My original patch RFC didn't include the imx8mn node, because it
> > > > > > > > > hangs, but the node I added looks like:
> > > > > > > > > 
> > > > > > > > > media_blk_ctl: clock-controller@32e28000 {
> > > > > > > > >      compatible = "fsl,imx8mn-media-blk-ctl", "syscon";
> > > > > > > > >      reg = <0x32e28000 0x1000>;
> > > > > > > > >      #clock-cells = <1>;
> > > > > > > > >      #reset-cells = <1>;
> > > > > > > > > };
> > > > > > > > > 
> > > > > > > > > I was hoping you might have some feedback on the 8mn clk-blk driver
> > > > > > > > > since you did the 8mp clk-blk drive and they appear to be very
> > > > > > > > > similar.
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > I'll do you one better still. I'll apply the patch in my tree and give it
> > > > > > > > a test tomorrow morning.
> > > > > > 
> > > > > > I do have some more updates on how to get the system to not hang, and
> > > > > > to enumerate more clocks.
> > > > > > Looking at Marek's work on enabling clocks in the 8MM, he added a
> > > > > > power-domain in dispmix_blk_ctl pointing to the dispmix in the GPC.
> > > > > > By forcing the GPC driver to write 0x1fff  to 32e28004, 0x7f to
> > > > > > 32e28000 and 0x30000 to 32e28008, the i.MX8MM can bring the display
> > > > > > clocks out of reset.
> > > > > > 
> > > > > 
> > > > > Yeah, that makes sense. Basically, it was trying to disable unused clocks
> > > > > (see clk_disable_unused) but in order to disable the clocks from the
> > > > > media BLK_CTL (which I think should be renamed in display BLK_CTL) the
> > > > > PD need to be on. Since you initially didn't give it any PD, it was trying
> > > > > to blindly write/read the gate bit and therefore freeze.
> > > > > 
> > > > > > Unfortunately, the i.MX8MN needs to have 0x100 written to both
> > > > > > 32e28000 and 32e28004, and the values written for the 8MM are not
> > > > > > compatible.
> > > > > > By forcing the GPC to write those values, I can get  lcdif_pixel_clk
> > > > > > and the mipi_dsi_clkref  appearing on the Nano.
> > > > > 
> > > > > I'm trying to make a branch with all the patches for all i.MX8M so I
> > > > > can keep track of it all. On this branch I've also applied the
> > > > > following patchset from Lucas Stach:
> > > > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Farm-kernel%2Fmsg843007.html&amp;data=04%7C01%7Cabel.vesa%40nxp.com%7C7ee028d464cf451e0e2d08d87c0177cd%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637395693031971288%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=yKGtS%2FTyKjGHZ2xcXSI8%2F74R9vUjPmXgT9FSQfUfZB4%3D&amp;reserved=0
> > > > > but I'm getting the folowing errors:
> > > > > 
> > > > > [   16.690885] imx-pgc imx-pgc-domain.3: failed to power up ADB400
> > > > > [   16.716839] imx-pgc imx-pgc-domain.3: failed to power up ADB400
> > > > > [   16.730500] imx-pgc imx-pgc-domain.3: failed to power up ADB400
> > > > > 
> > > > > Lucas, any thoughts?
> > > > > 
> > > > > Maybe it's something related to 8MN.
> > > > > 
> > > > I will go back and double check this now that we have both the
> > > > blt_crl->power-domain and the power-domain->blk_ctl.
> > > > 
> > > > > Will dig further, see what pops out.
> > > > 
> > > > I wasn't sure which direction to go with the name.  I can rename the
> > > > media_blk_ctl  driver to display_blk_ctl.  I used Media based on the
> > > > imx8mp naming convention and the fact that it's controlling both the
> > > > display and the camera interface, however it's depending on the
> > > > dispmix GPC.
> > > > 
> > > > I'll submit a RFC V2 with the cross referencing to the GPC based on
> > > > Marek's Mini patch set, but we'll still have an issue where the Mini
> > > > and Nano have different syscon values to enable the clocks, and
> > > > Marek's branch has it card-coded, so my patch would effectively break
> > > > the Mini in order to make the Nano operate until we find a better
> > > > solution.
> > > 
> > > The GPC should not write into the BLK_CTL region via syscon, but
> > > instead use the clocks and resets as exposed by the BLK_CTL driver.
> > > Doing it via syscon is a hack to get things going. The clocks and
> > > resets should properly be hooked up to the GPC domains via the clocks
> > > and resets DT properties.
> > > 
> > > For the clocks there is one complication: if the clocks are controlled
> > > via BLK_CTL we can only enable them once the domain is powered up,
> > > however the earlier designs using the GPCv2 assert resets as part of
> > > the power up sequence, which needs the clocks to be running for the
> > > reset to propagate. So depending on whether we have a power domain with
> > > a BLK_CTL or not we need to enable the clocks before or after powering
> > > up the domain. I guess we need a new DT property to specify which way
> > > the domain needs to handled.
> > 
> > So in the case of Nano, could we create two blocks instead of one?
> > The first block would enable the bus clock and reset that correspond
> > to writing 0x100 to avoid writing to syscon.  From there, we reference
> > that reset and clock from the GPC displaymix_pd to enable the access.
> > Once that's done, we point the 2nd block power-domain to the
> > dispmix_pd to unlock the remaining clocks.
> > 
> > Would that work?  I can try it later today, but I'm not near the hardware now.
> 
> Splitting the PD into 2 staged domains might actually work well to get
> around the cyclic dependency between GPC and BLK_CTL. It's not totally
> to my liking, as the DT description doesn't map 1:1 to hardware
> anymore, but it seems to be the most elegant solution to get around the
> dependency.
> 
> I'll try to implement this on the i.MX8MM today or tomorrow to see if
> it holds up in reality or if there are some hidden warts.
> 

I started looking into this yesterday, on 8MN. Splitting doesn't solve the issue.
I tried splitting into dispmix and dispmix_adb400. Added the bus_blk reset and
clock to the dispmix_adb400 PD. Trouble is, you can't add the dispmix_adb400 PD
to the blk_ctl because of the cyclic dependency.

> Regards,
> Lucas
>