linux-kernel - Re: [RFC 2/2] mmc: sdhci-pci: Use ACPI to get max frequency for Intel byt sdio host controller sub-vended by NI

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Date:   Wed, 9 Nov 2016 10:08:29 -0600
From:   Zach Brown <zach.brown@...com>
To:     Adrian Hunter <adrian.hunter@...el.com>
CC:     <ulf.hansson@...aro.org>, <linux-mmc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 2/2] mmc: sdhci-pci: Use ACPI to get max frequency for
 Intel byt sdio host controller sub-vended by NI

On Wed, Nov 09, 2016 at 03:24:24PM +0200, Adrian Hunter wrote:
> On 08/11/16 22:07, Zach Brown wrote:
> > On NI 9037 boards the max SDIO frequency is limited by trace lengths
> > and other layout choices. The max SDIO frequency is stored in an ACPI
> > table, as MXFQ.
> >
> > The driver reads the ACPI entry MXFQ during sdio_probe_slot and sets the
> > f_max field of the host with it.
> >
> > Signed-off-by: Nathan Sullivan <nathan.sullivan@...com>
> > Reviewed-by: Jaeden Amero <jaeden.amero@...com>
> > Reviewed-by: Josh Cartwright <joshc@...com>
> > Signed-off-by: Zach Brown <zach.brown@...com>
> > ---
> >  drivers/mmc/host/sdhci-pci-core.c | 30 ++++++++++++++++++++++++++++++
> >  1 file changed, 30 insertions(+)
> >
> > diff --git a/drivers/mmc/host/sdhci-pci-core.c b/drivers/mmc/host/sdhci-pci-core.c
> > index c333ce2..4ac7f16 100644
> > --- a/drivers/mmc/host/sdhci-pci-core.c
> > +++ b/drivers/mmc/host/sdhci-pci-core.c
> > @@ -27,6 +27,7 @@
> >  #include <linux/pm_runtime.h>
> >  #include <linux/mmc/slot-gpio.h>
> >  #include <linux/mmc/sdhci-pci-data.h>
> > +#include <linux/acpi.h>
> >
> >  #include "sdhci.h"
> >  #include "sdhci-pci.h"
> > @@ -377,6 +378,35 @@ static int byt_emmc_probe_slot(struct sdhci_pci_slot *slot)
> >
> >  static int ni_byt_sdio_probe_slot(struct sdhci_pci_slot *slot)
> >  {
> > +#ifdef CONFIG_ACPI
> > +	/* Get max freq from ACPI for NI hardware */
> > +	acpi_handle acpi_hdl;
> > +	acpi_status status;
> > +	struct acpi_buffer acpi_result = {
> > +		ACPI_ALLOCATE_BUFFER, NULL };
> > +	union acpi_object *acpi_buffer;
> > +	int max_freq;
> > +
> > +	status = acpi_get_handle(ACPI_HANDLE(&slot->chip->pdev->dev), "MXFQ",
> > +				 &acpi_hdl);
>
> Is "MXFQ" an object that has already been deployed or are you inventing it
> now?  In the latter case, did you consider device properties as an alternative?
>
"MXFQ" is an object that we have already deployed on some of our devices.

> > +	if (ACPI_FAILURE(status))
> > +		return  -ENODEV;
> > +
> > +	status = acpi_evaluate_object(acpi_hdl, NULL,
> > +				      NULL, &acpi_result);
> > +	if (ACPI_FAILURE(status))
> > +		return -EINVAL;
> > +
> > +	acpi_buffer = (union acpi_object *)acpi_result.pointer;
> > +
> > +	if (acpi_buffer->type != ACPI_TYPE_INTEGER)
> > +		return -EINVAL;
> > +
> > +	max_freq = acpi_buffer->integer.value;
> > +
> > +	slot->host->mmc->f_max = max_freq * 1000000;
> > +#endif
> > +
> >  	slot->host->mmc->caps |= MMC_CAP_POWER_OFF_CARD | MMC_CAP_NONREMOVABLE;
> >  	return 0;
> >  }
> >
>