On Tue, 12 Sept 2023 at 21:30, Janne Grunau via B4 Relay
wrote:
>
> From: Janne Grunau
>
> Multiple power domains need to be handled explicitly in each driver. The
> driver core can not handle it automatically since it is not aware of
> power sequencing requirements the hardware might have. This is not a
> problem for simpledrm since everything is expected to be powered on by
> the bootloader. simpledrm has just ensure it remains powered on during
> its lifetime.
> This is required on Apple silicon M2 and M2 Pro/Max/Ultra desktop
> systems. The HDMI output initialized by the bootloader requires keeping
> the display controller and a DP phy power domain on.
>
> Signed-off-by: Janne Grunau
Reviewed-by: Eric Curtin
Is mise le meas/Regards,
Eric Curtin
> ---
> Changes in v2:
> - removed broken drm_err() log statement only ment for debugging
> - removed commented cast
> - use correct format spcifier for 'int' in log statement
> - add 'continue;' after failure to get device for power_domain
> - use drm_warn() in non fatal error cases
> - removed duplicate PTR_ERR conversion
> - Link to v1:
> https://lore.kernel.org/r/20230910-simpledrm-multiple-power-domains-v1-1-f8718aefc...@jannau.net
> ---
> drivers/gpu/drm/tiny/simpledrm.c | 105
> +++
> 1 file changed, 105 insertions(+)
>
> diff --git a/drivers/gpu/drm/tiny/simpledrm.c
> b/drivers/gpu/drm/tiny/simpledrm.c
> index ff86ba1ae1b8..9c597461d1e2 100644
> --- a/drivers/gpu/drm/tiny/simpledrm.c
> +++ b/drivers/gpu/drm/tiny/simpledrm.c
> @@ -6,6 +6,7 @@
> #include
> #include
> #include
> +#include
> #include
>
> #include
> @@ -227,6 +228,12 @@ struct simpledrm_device {
> unsigned int regulator_count;
> struct regulator **regulators;
> #endif
> + /* power-domains */
> +#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
> + int pwr_dom_count;
> + struct device **pwr_dom_devs;
> + struct device_link **pwr_dom_links;
> +#endif
>
> /* simplefb settings */
> struct drm_display_mode mode;
> @@ -468,6 +475,101 @@ static int simpledrm_device_init_regulators(struct
> simpledrm_device *sdev)
> }
> #endif
>
> +#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
> +/*
> + * Generic power domain handling code.
> + *
> + * Here we handle the power-domains properties of our "simple-framebuffer"
> + * dt node. This is only necessary if there is more than one power-domain.
> + * A single power-domains is handled automatically by the driver core.
> Multiple
> + * power-domains have to be handled by drivers since the driver core can't
> know
> + * the correct power sequencing. Power sequencing is not an issue for
> simpledrm
> + * since the bootloader has put the power domains already in the correct
> state.
> + * simpledrm has only to ensure they remain active for its lifetime.
> + *
> + * When the driver unloads, we detach from the power-domains.
> + *
> + * We only complain about errors here, no action is taken as the most likely
> + * error can only happen due to a mismatch between the bootloader which set
> + * up the "simple-framebuffer" dt node, and the PM domain providers in the
> + * device tree. Chances are that there are no adverse effects, and if there
> are,
> + * a clean teardown of the fb probe will not help us much either. So just
> + * complain and carry on, and hope that the user actually gets a working fb
> at
> + * the end of things.
> + */
> +static void simpledrm_device_detach_genpd(void *res)
> +{
> + int i;
> + struct simpledrm_device *sdev = res;
> +
> + if (sdev->pwr_dom_count <= 1)
> + return;
> +
> + for (i = sdev->pwr_dom_count - 1; i >= 0; i--) {
> + if (!sdev->pwr_dom_links[i])
> + device_link_del(sdev->pwr_dom_links[i]);
> + if (!IS_ERR_OR_NULL(sdev->pwr_dom_devs[i]))
> + dev_pm_domain_detach(sdev->pwr_dom_devs[i], true);
> + }
> +}
> +
> +static int simpledrm_device_attach_genpd(struct simpledrm_device *sdev)
> +{
> + struct device *dev = sdev->dev.dev;
> + int i;
> +
> + sdev->pwr_dom_count = of_count_phandle_with_args(dev->of_node,
> "power-domains",
> +
> "#power-domain-cells");
> + /*
> +* Single power-domain devices are handled by driver core nothing to
> do
> +* here. The same for device nodes without "power-domains"
