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

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Date:   Wed, 25 Jan 2017 20:17:46 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Ingo Molnar <mingo@...nel.org>
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

Hi,

On 01/25/2017 05:23 PM, Ingo Molnar wrote:
> * 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?
>

Sure. I will move this to arch/x86/kernel/setup.c.

Best regards,
Lu Baolu