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 10:33:19 +0100
From:   Anisse Astier <anisse@...ier.eu>
To:     Adrian Hunter <adrian.hunter@...el.com>
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 Mon, Nov 19, 2018 at 09:45:03AM +0200, Adrian Hunter wrote:
> 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.

I just thought this message was a bit clearer than:
mmc0: intel_start_signal_voltage_switch DSM fn 4 error -95 result 0

But you're correct, with dynamic debug it shouldn't be an issue, and the
original message is easily searchable in the code. It only happens every
two seconds.

I'm ok to drop this patch.

Regards,

Anisse