linux-kernel - Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability

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Date:   Wed, 25 Jan 2017 10:23:55 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman <mathias.nyman@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, tglx@...utronix.de,
        peterz@...radead.org, linux-usb@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability


* Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> > Hiding essentially an early udelay() implementation in an early-printk driver is 
> > ugly and counterproductive.
> 
> Sure. How about below change?
> 
> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
> index d3f0c84..940989e 100644
> --- a/drivers/usb/early/xhci-dbc.c
> +++ b/drivers/usb/early/xhci-dbc.c
> @@ -587,6 +587,35 @@ static int xdbc_bulk_transfer(void *data, int size, bool read)
>         return size;
>  }
>  
> +static void __init xdbc_udelay_calibration(void)
> +{
> +       unsigned long lpj = 0;
> +       unsigned int tsc_khz, cpu_khz;
> +
> +       if (!boot_cpu_has(X86_FEATURE_TSC))
> +               goto calibration_out;
> +
> +       cpu_khz = x86_platform.calibrate_cpu();
> +       tsc_khz = x86_platform.calibrate_tsc();
> +
> +       if (tsc_khz == 0)
> +               tsc_khz = cpu_khz;
> +       else if (abs(cpu_khz - tsc_khz) * 10 > tsc_khz)
> +               cpu_khz = tsc_khz;
> +
> +       if (!tsc_khz)
> +               goto calibration_out;
> +
> +       lpj = tsc_khz * 1000;
> +       do_div(lpj, HZ);
> +
> +calibration_out:
> +       if (!lpj)
> +               lpj = 1 << 22;
> +
> +       loops_per_jiffy = lpj;
> +}
> +
>  static int __init xdbc_early_setup(void)
>  {
>         int ret;
> @@ -686,6 +715,8 @@ int __init early_xdbc_parse_parameter(char *s)
>         }
>         xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
>  
> +       xdbc_udelay_calibration();
> +
>         return 0;
>  }

Yeah - so could we do this in a more generic fashion, not in the early-printk 
driver but in core x86 code?

Thanks,

	Ingo