From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9E136207656 for ; Wed, 5 Mar 2025 23:06:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741215976; cv=none; b=gReWqI1EeiCFygEBgfPHNyUkngYv7O+NgK8IHKlAlJhNW2PppdiFiboDcV/BOM9QWURWfoEOtkeOtVk4AhQp9oMPsUNJFsbN10f6YZjZ2xCvwSVnpE+HSe+L70u08POwhxf0d6h8u9CIOYi7wzhUuAdJtaJbE48Ju1B546v6JLE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741215976; c=relaxed/simple; bh=wXdRvD9RVoL/20e9N8RG7TIk6vR62xBL1e5ehXXkOH0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oV9TPLOyWp7Jg17ix161kGC0pJ8fwgbYmKAtd0oYPBk0yp9v8iUEfOFIelF+5fFMlpWn1+/Mta0wqvWTOQkarFDML8txHbKzEv9eR6qhdJqJWeCUcRRhp7bZgzahPxamHL+pR+qbwZBx1p+X3SUyWHalapSA96kx84SLJQ2S48Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=cGh9lW8g; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cGh9lW8g" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741215973; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=OnVLYW2FIG18ZU9j87EnxxPDzjwGXevU3H0JDILigMI=; b=cGh9lW8gSuBu0gdI1AWAXqqmYvtQuHAtaJahL3mPblGnaZJmEoSrvV6O74DpDtGfcE9RQ8 JuE5xtCDtR1ZtDH4Hut4d1ggW/9Swf3CSGAHcyHYzsgX1F6P9Zg40S2HLYy8OtYo/Q2xPy ryqL0GuOaZLQqZLXAKYGPQeembcDPVw= Received: from mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-80-iYOOLzw8P96mzlZ7Xt0KiQ-1; Wed, 05 Mar 2025 18:05:57 -0500 X-MC-Unique: iYOOLzw8P96mzlZ7Xt0KiQ-1 X-Mimecast-MFC-AGG-ID: iYOOLzw8P96mzlZ7Xt0KiQ_1741215954 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2AACB1955DCD; Wed, 5 Mar 2025 23:05:54 +0000 (UTC) Received: from chopper.redhat.com (unknown [10.22.88.81]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 133B7300019E; Wed, 5 Mar 2025 23:05:49 +0000 (UTC) From: Lyude Paul To: dri-devel@lists.freedesktop.org, rust-for-linux@vger.kernel.org Cc: Danilo Krummrich , mcanal@igalia.com, Alice Ryhl , Maxime Ripard , Simona Vetter , Daniel Almeida , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?= , Benno Lossin , Andreas Hindborg , Trevor Gross , Asahi Lina , Wedson Almeida Filho , linux-kernel@vger.kernel.org (open list) Subject: [RFC v3 09/33] rust: drm/kms: Add DriverConnector::get_mode callback Date: Wed, 5 Mar 2025 17:59:25 -0500 Message-ID: <20250305230406.567126-10-lyude@redhat.com> In-Reply-To: <20250305230406.567126-1-lyude@redhat.com> References: <20250305230406.567126-1-lyude@redhat.com> Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Next up is filling out some of the basic connector hotplugging callbacks - which we'll need for setting up the fbdev helpers for KMS devices. Note that connector hotplugging in DRM follows a BFL scheme: pretty much all probing is protected under the mighty drm_device->mode_config.lock, which of course is a bit counter-intuitive to rust's locking schemes where data is always associated with its lock. Since that lock is embedded in an FFI type and not a rust type, we need to introduce our own wrapper type that acts as a lock acquisition for this. This brings us to introducing a few new types: * ModeConfigGuard - the most basic lock guard, as long as this object is alive we are guaranteed to be holding drm_device->mode_config.lock. This object doesn't do much else on its own currently. * ConnectorGuard - an object which corresponds to a specific typed DRM connector. This can only be acquired with a ModeConfigGuard, and will be used to allow calling methods that are only safe to call with drm_device->mode_config.lock held. Since it implements Deref> as well, it can also be used for any other operations that would normally be available on a DRM connector. And finally, we add the DriverConnector::get_modes() trait method which drivers can use to implement the drm_connector_helper_funcs.get_modes callback. Note that while we make this trait method mandatory, we only do so for the time being since VKMS doesn't do very much with DRM connectors - and as such we have no need yet to implement alternative connector probing schemes outside of get_modes(). Signed-off-by: Lyude Paul --- V3: * Document uses of ManuallyDrop * Use addr_of_mut!() instead of &mut * Add some missing invariant comments Signed-off-by: Lyude Paul --- rust/bindings/bindings_helper.h | 1 + rust/kernel/drm/kms.rs | 90 +++++++++++++++++++++++++++++++- rust/kernel/drm/kms/connector.rs | 62 ++++++++++++++++++++-- 3 files changed, 147 insertions(+), 6 deletions(-) diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index a6735f6fba947..27828dd36d4f2 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -21,6 +21,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs index f0044d396e1eb..7935e935f9975 100644 --- a/rust/kernel/drm/kms.rs +++ b/rust/kernel/drm/kms.rs @@ -8,15 +8,20 @@ pub mod plane; use crate::{ - device, + container_of, device, drm::{device::Device, drv::Driver}, error::to_result, prelude::*, private::Sealed, + sync::{Mutex, MutexGuard}, types::*, }; use bindings; -use core::{marker::PhantomData, ops::Deref, ptr::NonNull}; +use core::{ + marker::PhantomData, + ops::Deref, + ptr::{self, addr_of_mut, NonNull}, +}; /// The C vtable for a [`Device`]. /// @@ -191,6 +196,23 @@ pub struct ModeConfigInfo { pub preferred_fourcc: Option, } +impl Device { + /// Retrieve a pointer to the mode_config mutex + #[inline] + pub(crate) fn mode_config_mutex(&self) -> &Mutex<()> { + // SAFETY: This lock is initialized for as long as `Device` is exposed to users + unsafe { Mutex::from_raw(addr_of_mut!((*self.as_raw()).mode_config.mutex)) } + } + + /// Acquire the [`mode_config.mutex`] for this [`Device`]. + #[inline] + pub fn mode_config_lock(&self) -> ModeConfigGuard<'_, T> { + // INVARIANT: We're locking mode_config.mutex, fulfilling our invariant that this lock is + // held throughout ModeConfigGuard's lifetime. + ModeConfigGuard(self.mode_config_mutex().lock(), PhantomData) + } +} + /// A modesetting object in DRM. /// /// This is any type of object where the underlying C object contains a [`struct drm_mode_object`]. @@ -314,3 +336,67 @@ unsafe fn dec_ref(obj: NonNull) { unsafe { bindings::drm_mode_object_put(obj.as_ref().raw_mode_obj()) } } } + +/// A mode config guard. +/// +/// This is an exclusive primitive that represents when [`drm_device.mode_config.mutex`] is held - as +/// some modesetting operations (particularly ones related to [`connectors`](connector)) are still +/// protected under this single lock. The lock will be dropped once this object is dropped. +/// +/// # Invariants +/// +/// - `self.0` is contained within a [`struct drm_mode_config`], which is contained within a +/// [`struct drm_device`]. +/// - The [`KmsDriver`] implementation of that [`struct drm_device`] is always `T`. +/// - This type proves that [`drm_device.mode_config.mutex`] is acquired. +/// +/// [`struct drm_mode_config`]: (srctree/include/drm/drm_device.h) +/// [`drm_device.mode_config.mutex`]: (srctree/include/drm/drm_device.h) +/// [`struct drm_device`]: (srctree/include/drm/drm_device.h) +pub struct ModeConfigGuard<'a, T: KmsDriver>(MutexGuard<'a, ()>, PhantomData); + +impl<'a, T: KmsDriver> ModeConfigGuard<'a, T> { + /// Construct a new [`ModeConfigGuard`]. + /// + /// # Safety + /// + /// The caller must ensure that [`drm_device.mode_config.mutex`] is acquired. + /// + /// [`drm_device.mode_config.mutex`]: (srctree/include/drm/drm_device.h) + pub(crate) unsafe fn new(drm: &'a Device) -> Self { + // SAFETY: Our safety contract fulfills the requirements of `MutexGuard::new()` + // INVARIANT: And our safety contract ensures that this type proves that + // `drm_device.mode_config.mutex` is acquired. + Self( + unsafe { MutexGuard::new(drm.mode_config_mutex(), ()) }, + PhantomData, + ) + } + + /// Return the [`Device`] that this [`ModeConfigGuard`] belongs to. + pub fn drm_dev(&self) -> &'a Device { + // SAFETY: + // - `self` is embedded within a `drm_mode_config` via our type invariants + // - `self.0.lock` has an equivalent data type to `mutex` via its type invariants. + let mode_config = unsafe { container_of!(self.0.lock, bindings::drm_mode_config, mutex) }; + + // SAFETY: And that `drm_mode_config` lives in a `drm_device` via type invariants. + unsafe { + Device::borrow(container_of!( + mode_config, + bindings::drm_device, + mode_config + )) + } + } + + /// Assert that the given device is the owner of this mode config guard. + /// + /// # Panics + /// + /// Panics if `dev` is different from the owning device for this mode config guard. + #[inline] + pub(crate) fn assert_owner(&self, dev: &Device) { + assert!(ptr::eq(self.drm_dev(), dev)); + } +} diff --git a/rust/kernel/drm/kms/connector.rs b/rust/kernel/drm/kms/connector.rs index 6fe0a7517bd55..14de3b0529f89 100644 --- a/rust/kernel/drm/kms/connector.rs +++ b/rust/kernel/drm/kms/connector.rs @@ -4,7 +4,7 @@ //! //! C header: [`include/drm/drm_connector.h`](srctree/include/drm/drm_connector.h) -use super::{encoder::*, KmsDriver, ModeObject, RcModeObject}; +use super::{encoder::*, KmsDriver, ModeConfigGuard, ModeObject, RcModeObject}; use crate::{ alloc::KBox, bindings, @@ -17,7 +17,7 @@ }; use core::{ marker::*, - mem, + mem::{self, ManuallyDrop}, ops::*, ptr::{addr_of_mut, null_mut}, stringify, @@ -106,7 +106,7 @@ pub trait DriverConnector: Send + Sync + Sized { destroy: Some(connector_destroy_callback::), force: None, detect: None, - fill_modes: None, + fill_modes: Some(bindings::drm_helper_probe_single_connector_modes), debugfs_init: None, oob_hotplug_event: None, atomic_duplicate_state: Some(atomic_duplicate_state_callback::), @@ -114,7 +114,7 @@ pub trait DriverConnector: Send + Sync + Sized { helper_funcs: bindings::drm_connector_helper_funcs { mode_valid: None, atomic_check: None, - get_modes: None, + get_modes: Some(get_modes_callback::), detect_ctx: None, enable_hpd: None, disable_hpd: None, @@ -145,6 +145,12 @@ pub trait DriverConnector: Send + Sync + Sized { /// /// Drivers may use this to instantiate their [`DriverConnector`] object. fn new(device: &Device, args: Self::Args) -> impl PinInit; + + /// Retrieve a list of available display modes for this [`Connector`]. + fn get_modes<'a>( + connector: ConnectorGuard<'a, Self>, + guard: &ModeConfigGuard<'a, Self::Driver>, + ) -> i32; } /// The generated C vtable for a [`DriverConnector`]. @@ -196,6 +202,21 @@ fn deref(&self) -> &Self::Target { } } +impl Connector { + /// Acquire a [`ConnectorGuard`] for this connector from a [`ModeConfigGuard`]. + /// + /// This verifies using the provided reference that the given guard is actually for the same + /// device as this connector's parent. + /// + /// # Panics + /// + /// Panics if `guard` is not a [`ModeConfigGuard`] for this connector's parent [`Device`]. + pub fn guard<'a>(&'a self, guard: &ModeConfigGuard<'a, T::Driver>) -> ConnectorGuard<'a, T> { + guard.assert_owner(self.drm_dev()); + ConnectorGuard(self) + } +} + /// A trait implemented by any type that acts as a [`struct drm_connector`] interface. /// /// This is implemented internally by DRM. @@ -392,6 +413,39 @@ pub fn attach_encoder(&self, encoder: &impl AsRawEncoder) -> Result { drop(unsafe { KBox::from_raw(connector as *mut Connector) }); } +unsafe extern "C" fn get_modes_callback( + connector: *mut bindings::drm_connector, +) -> core::ffi::c_int { + // SAFETY: This is safe via `DriverConnector`s type invariants. + let connector = unsafe { Connector::::from_raw(connector) }; + + // SAFETY: This FFI callback is only called while `mode_config.lock` is held + // We use ManuallyDrop here to prevent the lock from being released after the callback + // completes, as that should be handled by DRM. + let guard = ManuallyDrop::new(unsafe { ModeConfigGuard::new(connector.drm_dev()) }); + + T::get_modes(connector.guard(&guard), &guard) +} + +/// A privileged [`Connector`] obtained while holding a [`ModeConfigGuard`]. +/// +/// This provides access to various methods for [`Connector`] that must happen under lock, such as +/// setting resolution preferences and adding display modes. +/// +/// # Invariants +/// +/// Shares the invariants of [`ModeConfigGuard`]. +#[derive(Copy, Clone)] +pub struct ConnectorGuard<'a, T: DriverConnector>(&'a Connector); + +impl Deref for ConnectorGuard<'_, T> { + type Target = Connector; + + fn deref(&self) -> &Self::Target { + self.0 + } +} + // SAFETY: DRM expects this struct to be zero-initialized unsafe impl Zeroable for bindings::drm_connector_state {} -- 2.48.1