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

[Abel Vesa]

On 20-10-26 16:37:51, Lucas Stach wrote:
> Am Montag, den 26.10.2020, 16:55 +0200 schrieb Abel Vesa:
> > 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://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.spinics.net%2Flists%2Farm-kernel%2Fmsg843007.html&data=04%7C01%7Cabel.vesa%40nxp.com%7Cc930b0f523c44946a93f08d879c51c3f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637393234789815116%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ZzzUpEiEVcWqQQ5azAx8dkjHgiSMwkK04tqi32uLKbU%3D&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.
> 
> The ADB is apparently clocked by one of the BLK_CTL clocks, so the ADB
> handshake ack will only work when the BLK_CTL clocks are enabled. So I
> guess the GPC driver should enable those clocks and assert the resets
> at the right time in the power-up sequencing. Unfortunately this means
> we can't properly put the BLK_CTL driver in the power-domain without
> having a cyclic dependency in the DT. I'm still thinking about how to
> solve this properly.
> 

I remember we had something similar in our internal tree with the
bus_blk_clk on 8MP, which was added by the media BLK_CTL. What I did was to
just drop the registration of that clock entirely. My rationale was that if
the clock is part of the BLK_CTL but also needed by the BLK_CTL to work,
I can leave it alone (that is, enabled by default) since when the PD will be
powered off the clock will gated too. I guess another option would be to 
mark it as critical, that way, it will never be disabled (will be left alone
by the clk_disable_unused too) but at the same time will be visible in the
clock hierarchy.

> Regards,
> Lucas
>