[RFC 0/3] clk: imx: Implement blk-ctl driver for i.MX8MN

[Lucas Stach]

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 at 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 at 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 at 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 at 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://www.spinics.net/lists/arm-kernel/msg843007.html
> > > > 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.

Regards,
Lucas