linux-kernel - Re: [PATCH v2 3/3] mmc: sdhci-pci: only install voltage switch method when useful

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Date:   Mon, 19 Nov 2018 09:45:03 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Anisse Astier <anisse@...ier.eu>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mmc: sdhci-pci: only install voltage switch method
 when useful

On 16/11/18 6:58 PM, Anisse Astier wrote:
> Hi Adrian,
> 
> On Tue, Oct 23, 2018 at 12:07:29PM +0200, Anisse Astier wrote:
>> If there's no ACPI DSM for voltage switch, it will just cause a lot of
>> debug info down the line, we only need one at startup.
>>
>> Signed-off-by: Anisse Astier <anisse@...ier.eu>
>> ---
>>  drivers/mmc/host/sdhci-pci-core.c | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
>> index f2c1fb339d66..95fdbb883c7e 100644
>> --- a/drivers/mmc/host/sdhci-pci-core.c
>> +++ b/drivers/mmc/host/sdhci-pci-core.c
>> @@ -723,6 +723,7 @@ static const struct dmi_system_id board_no_1_8v[] = {
>>  static void byt_probe_slot(struct sdhci_pci_slot *slot)
>>  {
>>  	struct mmc_host_ops *ops = &slot->host->mmc_host_ops;
>> +	struct intel_host *intel_host = sdhci_pci_priv(slot);
>>  
>>  	byt_read_dsm(slot);
>>  
>> @@ -733,6 +734,16 @@ static void byt_probe_slot(struct sdhci_pci_slot *slot)
>>  				mmc_hostname(slot->host->mmc));
>>  		slot->host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>>  	}
>> +	/* Check if we have the appropriate voltage switch DSM methods */
>> +	if (!(intel_host->dsm_fns & (1 << INTEL_DSM_V18_SWITCH)) &&
>> +	    !(intel_host->dsm_fns & (1 << INTEL_DSM_V33_SWITCH))) {
>> +		/* No voltage switching supported at all, there's no
>> +		 * point in installing the callback: return.
>> +		 */
>> +		pr_debug("%s: No voltage switching ACPI DSM helper\n",
>> +				mmc_hostname(slot->host->mmc));
>> +		return;
>> +	}
>>  	ops->start_signal_voltage_switch = intel_start_signal_voltage_switch;
>>  }
>>  
>> -- 
>> 2.17.2
>>
> 
> What do you think of picking this last patch ? Or maybe you had
> different cleanups in mind when you said you wanted to rework this ?

Voltage switches are relatively rare, and dynamic debug allows control over
exactly which debug messages display, so I am not sure this patch is needed.