Re: [PATCH] clk: imx25: set correct parents for ssi ipg clocks

["Lothar Waßmann" <LW@KARO-electronics.de>]

Hi,

On Thu, 8 Mar 2018 17:46:54 +0100 Martin Kaiser wrote:
> Hi Fabio,
> 
> thanks for the quick response.
> 
> Thus wrote Fabio Estevam (festevam@gmail.com):
> 
> > Hi Martin,
> 
> > On Thu, Mar 8, 2018 at 11:08 AM, Martin Kaiser <martin@kaiser.cx> wrote:
> > > Hi Fabio,
> 
> > > Thus wrote Fabio Estevam (festevam@gmail.com):
> 
> > >> I get audio working from SSI1, but I guess this is due to the fact
> > >> that the bootloader enables the SSI clock:
> 
> > >> I have the following in U-Boot:
> 
> > >> /* Enable the clocks */
> > >> DATA 4 0x53f8000c 0x1fffffff
> > >> DATA 4 0x53f80010 0xffffffff
> > >> DATA 4 0x53f80014 0xfdfff
> 
> > > I'm using the same initial settings.
> 
> > > Nevertheless, ssi1_ipg_per is disbled after loading the kernel.
> 
> > > Digging into this a bit more, it turned out that without my patch,
> > > clk_disable_unused() recognizes ssi1_ipg_per as unused and disables it.
> 
> > > If my patch is applied and ssi1_ipg_per is declared as parent of
> > > ssi1_ipg, clk_disable_unused() will not disable it and fsl_ssi_startup()
> > > will enable both ssi1_ipg_per and ssi1_ipg before playing sound.
> 
> > I can get audio to work fine without your patch on a mx25pdk.
> 
> this is surprising. How come the ssi1_ipg_per clock is not turned off by
> clk_disable_unused()? Where is it used? Do you have
> 
> <&clks 55>
> 
> anywhere in your DT?
> 
> > In the other i.MX clock drivers we have this same pattern:
> 
> > clks[IMX6SL_CLK_SSI1_IPG]     = imx_clk_gate2_shared("ssi1_ipg",     "ipg",
> 
> It seems to the that imx25 uses a different clock hierarchy for ssi than other
> imx chips.
> 
> Documentation/devicetree/bindings/clock/imx25-clock.txt: ssi1_ipg_per      55
> Documentation/devicetree/bindings/clock/imx25-clock.txt: ssi2_ipg_per      56
> Documentation/devicetree/bindings/clock/imx25-clock.txt: ssi1_ipg    117
> Documentation/devicetree/bindings/clock/imx25-clock.txt: ssi2_ipg    118
> Documentation/devicetree/bindings/clock/imx31-clock.txt: ssi1_gate            32
> Documentation/devicetree/bindings/clock/imx31-clock.txt: ssi2_gate            52
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi_sel        22
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi1_div_pre      23
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi1_div_post     24
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi2_div_pre      25
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi2_div_post     26
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi1_gate      68
> Documentation/devicetree/bindings/clock/imx35-clock.txt: ssi2_gate      69
> 
> Others don't have ssiX_ipg_per.
> 
> > It is not clear to me what is the real issue this patch is trying to fix.
> 
> True. This needs clarification.
> 
> I found that, in oder to get a tx clock out of the SSI, both ssi1_ipg_per and
> ssi1_ipg clocks must be active.
> 
> The fsl_ssi driver only activates ssi1_ipg.
> 
> If I activate ssi1_ipg_per in the bootloader, clk_disable_unused() deactivates it.
> 
> (My codec chip does not use a dedicated clock line. It takes the bit clock that
> is the output of SSI. Are you maybe using ssi1_ipg_per for your codec and
> enable it there?)
> 
> In my first mail, I was wondering about imx25 uart1, where we also have
> uart1_ipg and uart_ipg_per and the clock seeting is
> 
>    clk[uart1_ipg] = imx_clk_gate("uart1_ipg", "ipg", ccm(CCM_CGCR2), 14);
> 
> In this case, both uart1 and uart_ipg_per are listed in the device tree
> 
>          uart1: serial@43f90000 {                                                                                                      
> ...
>             clocks = <&clks 120>, <&clks 57>;                                                                                          
>             clock-names = "ipg", "per";                                                                                                
>          };                                                                                                                            
> 
> Documentation/devicetree/bindings/clock/imx25-clock.txt
>    uart_ipg_per      57
>    uart1_ipg      120
> 
> and the driver enables both clocks explicitly. So they are not unused.
> 
> 
> Doing something like this is not an option for ssi, this will not work with
> imx31, 35 etc.
> 
> Therefore, I suggest setting ssi1_ipg_per as parent of ssi1_ipg.
>
The right wayto fix this is to add the missing ipg_per clock to the DTB
rather than introducing a bogus clock relationship that doesn't exist
in hardware.
The sound/soc/fsl/fsl_ssi.c driver does already handle a second clock
as bitclock. It only needs to be specified in the DTB:
&ssi1 {
	clocks = <&clks 117>, <&clk 55>;
	clock-names = "ipg", "baud";
};


Lothar Waßmann