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

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Date:   Sun, 11 Mar 2018 17:39:46 +0100
From:   Martin Kaiser <martin@...ser.cx>
To:     Fabio Estevam <festevam@...il.com>,
        Lothar Waßmann <LW@...O-electronics.de>
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: imx25: set correct parents for ssi ipg clocks

Hi Fabio & Lothar,

Thus wrote Fabio Estevam (festevam@...il.com):

> On Thu, Mar 8, 2018 at 1:46 PM, Martin Kaiser <martin@...ser.cx> wrote:

> >> 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?

> No, I don't. imx25-pdk board operates SSI in slave mode.

> > (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?)

> The difference between our boards is that you use SSI in master mode
> and mx25pdk in slave mode.

> > 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@...90000 {
> > ...
> >             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.

> The solution to this is passing the "baud" clock as Lothar pointed out.

ok, I got your point now.

The ssi1_ipg clock does not depend on ssi1_ipg_per. This is in line with
the clock generation scheme in the reference manual.

And there's configurations where ssi1_ipg should be switched on, but not
ssi1_ipg_per.

I'll look into using the baud clock on my board.

Thanks to both of you for taking the time to explain this.

Best regards,

   Martin