linux-kernel - Re: [PATCH] platform/x86: intel_pmc: Ignore GBE LTR on Tiger Lake platforms

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Message-ID: <3e339312-f265-ce7e-dc70-253d1c93256d@redhat.com>
Date:   Sun, 7 Mar 2021 20:13:11 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Neftin, Sasha" <sasha.neftin@...el.com>,
        "David E. Box" <david.e.box@...ux.intel.com>,
        irenic.rajneesh@...il.com, mgross@...ux.intel.com
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH] platform/x86: intel_pmc: Ignore GBE LTR on Tiger Lake
 platforms

Hi,

On 3/7/21 9:39 AM, Neftin, Sasha wrote:
> On 3/5/2021 21:06, David E. Box wrote:
>> Due to a HW limitation, the Latency Tolerance Reporting (LTR) value
>> programmed in the Tiger Lake GBE controller is not large enough to allow
>> the platform to enter Package C10, which in turn prevents the platform from
>> achieving its low power target during suspend-to-idle.  Ignore the GBE LTR
>> value on Tiger Lake. LTR ignore functionality is currently performed solely
>> by a debugfs write call. Split out the LTR code into its own function that
>> can be called by both the debugfs writer and by this work around.
>>
>> Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
>> Reviewed-by: Sasha Neftin <sasha.neftin@...el.com>
>> Cc: intel-wired-lan@...ts.osuosl.org
>> ---
>>   drivers/platform/x86/intel_pmc_core.c | 55 ++++++++++++++++++++-------
>>   1 file changed, 42 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/platform/x86/intel_pmc_core.c b/drivers/platform/x86/intel_pmc_core.c
>> index ee2f757515b0..ab31eb646a1a 100644
>> --- a/drivers/platform/x86/intel_pmc_core.c
>> +++ b/drivers/platform/x86/intel_pmc_core.c
>> @@ -863,34 +863,45 @@ static int pmc_core_pll_show(struct seq_file *s, void *unused)
>>   }
>>   DEFINE_SHOW_ATTRIBUTE(pmc_core_pll);
>>   -static ssize_t pmc_core_ltr_ignore_write(struct file *file,
>> -                     const char __user *userbuf,
>> -                     size_t count, loff_t *ppos)
>> +static int pmc_core_write_ltr_ignore(u32 value)
>>   {
>>       struct pmc_dev *pmcdev = &pmc;
>>       const struct pmc_reg_map *map = pmcdev->map;
>> -    u32 val, buf_size, fd;
>> -    int err;
>> -
>> -    buf_size = count < 64 ? count : 64;
>> -
>> -    err = kstrtou32_from_user(userbuf, buf_size, 10, &val);
>> -    if (err)
>> -        return err;
>> +    u32 fd;
>> +    int err = 0;
>>         mutex_lock(&pmcdev->lock);
>>   -    if (val > map->ltr_ignore_max) {
>> +    if (fls(value) > map->ltr_ignore_max) {
>>           err = -EINVAL;
>>           goto out_unlock;
>>       }
>>         fd = pmc_core_reg_read(pmcdev, map->ltr_ignore_offset);
>> -    fd |= (1U << val);
>> +    fd |= value;
>>       pmc_core_reg_write(pmcdev, map->ltr_ignore_offset, fd);
>>     out_unlock:
>>       mutex_unlock(&pmcdev->lock);
>> +
>> +    return err;
>> +}
>> +
>> +static ssize_t pmc_core_ltr_ignore_write(struct file *file,
>> +                     const char __user *userbuf,
>> +                     size_t count, loff_t *ppos)
>> +{
>> +    u32 buf_size, val;
>> +    int err;
>> +
>> +    buf_size = count < 64 ? count : 64;
>> +
>> +    err = kstrtou32_from_user(userbuf, buf_size, 10, &val);
>> +    if (err)
>> +        return err;
>> +
>> +    err = pmc_core_write_ltr_ignore(1U << val);
>> +
>>       return err == 0 ? count : err;
>>   }
>>   @@ -1189,6 +1200,15 @@ static int quirk_xtal_ignore(const struct dmi_system_id *id)
>>       return 0;
>>   }
>>   +static int quirk_ltr_ignore(u32 val)
>> +{
>> +    int err;
>> +
>> +    err = pmc_core_write_ltr_ignore(val);
>> +
>> +    return err;
>> +}
>> +
>>   static const struct dmi_system_id pmc_core_dmi_table[]  = {
>>       {
>>       .callback = quirk_xtal_ignore,
>> @@ -1244,6 +1264,15 @@ static int pmc_core_probe(struct platform_device *pdev)
>>       pmcdev->pmc_xram_read_bit = pmc_core_check_read_lock_bit();
>>       dmi_check_system(pmc_core_dmi_table);
>>   +    /*
>> +     * On TGL, due to a hardware limitation, the GBE LTR blocks PC10 when
>> +     * a cable is attached. Tell the PMC to ignore it.
>> +     */
>> +    if (pmcdev->map == &tgl_reg_map) {
> I would suggest: if (pmcdev->map >= &tgl_reg_map)

Erm, no just no. tgl_reg_map is a global variable you can absolutely NOT rely
on the ordering of global variables in memory like this. Moreover using ordered
comparisons on pointers generally is a very bad idea, please don't.

Regards,

Hans