Re: [Patch v2 resend] apple-gmux: lock iGP IO to protect from vgaarb changes

Bjorn Helgaas
2015-03-09T22:11:27Z

On Mon, Mar 9, 2015 at 4:52 PM, Bruno Prémont <bonbons@linux-vserver.org> wrote:
> As GMUX depends on IO for iGP to be enabled and active, lock the IO at
> vgaarb level. This should prevent GPU driver for dGPU to disable IO for
> iGP while it tries to own legacy VGA IO.
>
> This fixes usage of backlight control combined with closed nvidia
> driver on some Apple dual-GPU (intel/nvidia) systems.
>
> On those systems loading nvidia driver disables intel IO decoding,
> disabling the gmux backlight controls as a side effect.
> Prior to commits moving boot_vga from (optional) efifb to less optional
> vgaarb this mis-behavior could be avoided by using right kernel config
> (efifb enabled but vgaarb disabled).
>
> This patch explicitly does not try to trigger vgaarb changes in order
> to avoid confusing already running graphics drivers. If IO has been
> mis-configured by vgaarb gmux will thus fail to probe.
> It is expected to load/probe gmux prior to graphics drivers.
>
> Fixes: ce027dac592c0ada241ce0f95ae65856828ac450 # nvidia interaction
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=86121
> Reported-by: Petri Hodju <petrihodju@yahoo.com>
> Tested-by: Petri Hodju <petrihodju@yahoo.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Matthew Garrett <matthew.garrett@nebula.com>
> Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
> ---
> Resending v2 in the hope Darren won't hit quoted-printable.
> Also adding linux-pci on CC by Bjorn's request in bugzilla.

The bugzilla is assigned to PCI, and I was just trying to resolve it.
But it looks like Darren might be the logical person to apply this, so
I'll ignore it unless poked again.

A few minor comments below.

> Changes since v1:
> - Dropped repeat of gmux in pr_info/pr_err calls
> - Mention PCI device we tried to lock IO for in case of error
>
>
> drivers/platform/x86/apple-gmux.c | 43 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
> index b9429fb..22da6a3 100644
> --- a/drivers/platform/x86/apple-gmux.c
> +++ b/drivers/platform/x86/apple-gmux.c
> @@ -22,6 +22,7 @@
> #include <linux/delay.h>
> #include <linux/pci.h>
> #include <linux/vga_switcheroo.h>
> +#include <linux/vgaarb.h>
> #include <acpi/video.h>
> #include <asm/io.h>
>
> @@ -31,6 +32,7 @@ struct apple_gmux_data {
> bool indexed;
> struct mutex index_lock;
>
> + struct pci_dev *pdev;
> struct backlight_device *bdev;
>
> /* switcheroo data */
> @@ -415,6 +417,22 @@ static int gmux_resume(struct device *dev)
> return 0;
> }
>
> +static struct pci_dev *gmux_find_pdev(void)
> +{
> + struct pci_dev *pdev = NULL;

Typical to have a blank line here (between local variables and code).

> + while ((pdev = pci_get_class(PCI_CLASS_DISPLAY_VGA << 8, pdev))) {
> + u16 cmd;
> +
> + pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> + if (!(cmd & PCI_COMMAND_IO))
> + continue;
> +
> + return pdev;

This returns a device with reference count incremented. The
convention in PCI, at least, is to name functions that acquire a
reference with "_get_", and functions that don't acquire a reference
with "_find_". So maybe this function should be renamed?

> + }
> +
> + return NULL;
> +}
> +
> static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
> {
> struct apple_gmux_data *gmux_data;
> @@ -425,6 +443,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
> int ret = -ENXIO;
> acpi_status status;
> unsigned long long gpe;
> + struct pci_dev *pdev = NULL;
>
> if (apple_gmux_data)
> return -EBUSY;
> @@ -475,7 +494,7 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
> ver_minor = (version >> 16) & 0xff;
> ver_release = (version >> 8) & 0xff;
> } else {
> - pr_info("gmux device not present\n");
> + pr_info("gmux device not present or IO disabled\n");
> ret = -ENODEV;
> goto err_release;
> }
> @@ -483,6 +502,23 @@ static int gmux_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
> pr_info("Found gmux version %d.%d.%d [%s]\n", ver_major, ver_minor,
> ver_release, (gmux_data->indexed ? "indexed" : "classic"));
>
> + /*
> + * Apple systems with gmux are EFI based and normally don't use
> + * VGA. In addition changing IO+MEM ownership between IGP and dGPU
> + * disables IO/MEM used for backlight control on some systems.
> + * Lock IO+MEM to GPU with active IO to prevent switch.
> + */
> + pdev = gmux_find_pdev();
> + if (pdev && vga_tryget(pdev,
> + VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM)) {
> + pr_err("IO+MEM vgaarb-locking for PCI:%s failed\n",
> + pci_name(pdev));

It'd be nice to use dev_info/dev_err() for all the messages here, but
I see the existing style is to just use pr_info()/pr_err(). So a
change to use the dev_ functions would be out of scope for the bug fix
itself, but possibly a useful follow-on.

> + ret = -EBUSY;
> + goto err_release;
> + } else if (pdev)
> + pr_info("locked IO for PCI:%s\n", pci_name(pdev));
> + gmux_data->pdev = pdev;
> +
> memset(&props, 0, sizeof(props));
> props.type = BACKLIGHT_PLATFORM;
> props.max_brightness = gmux_read32(gmux_data, GMUX_PORT_MAX_BRIGHTNESS);
> @@ -574,6 +609,7 @@ err_enable_gpe:
> err_notify:
> backlight_device_unregister(bdev);
> err_release:
> + pci_dev_put(pdev);
> release_region(gmux_data->iostart, gmux_data->iolen);
> err_free:
> kfree(gmux_data);
> @@ -593,6 +629,11 @@ static void gmux_remove(struct pnp_dev *pnp)
> &gmux_notify_handler);
> }
>
> + if (gmux_data->pdev) {
> + vga_put(gmux_data->pdev,
> + VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM);
> + pci_dev_put(gmux_data->pdev);
> + }
> backlight_device_unregister(gmux_data->bdev);
>
> release_region(gmux_data->iostart, gmux_data->iolen);