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Wed, 13 May 2026 11:17:38 -0700 (PDT) MIME-Version: 1.0 References: <20260512-panthor-signal-from-irq-v2-0-95c614a739cb@collabora.com> <20260512-panthor-signal-from-irq-v2-4-95c614a739cb@collabora.com> <20260513100901.7b497929@fedora> <20260513193011.4c7d30fc@fedora> In-Reply-To: <20260513193011.4c7d30fc@fedora> From: Chia-I Wu Date: Wed, 13 May 2026 11:17:26 -0700 X-Gm-Features: AVHnY4ID2SS3qy5X2PgxDw2j_jo89uasHkOOqSnCyRLgpaR9zlwLs2FVokF5NnE Message-ID: Subject: Re: [PATCH v2 04/11] drm/panthor: Extend the IRQ logic to allow fast/hard IRQ handlers To: Boris Brezillon Cc: Steven Price , Liviu Dudau , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Wed, May 13, 2026 at 10:30=E2=80=AFAM Boris Brezillon wrote: > > On Wed, 13 May 2026 10:06:14 -0700 > Chia-I Wu wrote: > > > On Wed, May 13, 2026 at 1:09=E2=80=AFAM Boris Brezillon > > wrote: > > > > > > On Tue, 12 May 2026 12:11:08 -0700 > > > Chia-I Wu wrote: > > > > > > > On Tue, May 12, 2026 at 4:54=E2=80=AFAM Boris Brezillon > > > > wrote: > > > > > > > > > > All drivers except panthor signal their fences from their interru= pt > > > > > handler to minimize latency. We could do the same from the thread= ed > > > > > handler, but the latency is still quite high in that case, so let= 's > > > > > allow components to choose the context they want their IRQ handle= r > > > > > to run in by exposing support for custom hard handlers. > > > > > > > > > > Reviewed-by: Liviu Dudau > > > > > Reviewed-by: Steven Price > > > > > Signed-off-by: Boris Brezillon > > > > > --- > > > > > drivers/gpu/drm/panthor/panthor_device.h | 11 ++++++++--- > > > > > drivers/gpu/drm/panthor/panthor_fw.c | 1 + > > > > > drivers/gpu/drm/panthor/panthor_gpu.c | 1 + > > > > > drivers/gpu/drm/panthor/panthor_mmu.c | 1 + > > > > > drivers/gpu/drm/panthor/panthor_pwr.c | 1 + > > > > > 5 files changed, 12 insertions(+), 3 deletions(-) > > > > > > > > > > diff --git a/drivers/gpu/drm/panthor/panthor_device.h b/drivers/g= pu/drm/panthor/panthor_device.h > > > > > index 393fcda73d88..1aaf06df875b 100644 > > > > > --- a/drivers/gpu/drm/panthor/panthor_device.h > > > > > +++ b/drivers/gpu/drm/panthor/panthor_device.h > > > > > @@ -672,6 +672,7 @@ static inline void panthor_irq_disable_events= (struct panthor_irq *pirq, u32 mask > > > > > static inline int > > > > > panthor_irq_request(struct panthor_device *ptdev, struct panthor= _irq *pirq, > > > > > int irq, u32 mask, void __iomem *iomem, const= char *name, > > > > > + irqreturn_t (*raw_handler)(int, void *data), > > > > > irqreturn_t (*threaded_handler)(int, void *da= ta)) > > > > > { > > > > > const char *full_name; > > > > > @@ -687,9 +688,13 @@ panthor_irq_request(struct panthor_device *p= tdev, struct panthor_irq *pirq, > > > > > return -ENOMEM; > > > > > > > > > > panthor_irq_resume(pirq); > > > > > - return devm_request_threaded_irq(ptdev->base.dev, irq, > > > > > - panthor_irq_default_raw_= handler, > > > > > - threaded_handler, > > > > > + > > > > > + if (!threaded_handler) { > > > > > + return devm_request_irq(ptdev->base.dev, irq, raw= _handler, > > > > > + IRQF_SHARED, full_name, p= irq); > > > > > + } > > > > devm_request_irq expands to devm_request_threaded_irq plus > > > > IRQF_COND_ONESHOT. This appears redundant. > > > > > > I considered going for devm_request_threaded_irq(COND_ONESHOT), but I > > > thought it was easier to reason about with a regular devm_request_irq= () > > > and an extra conditional since request_irq() is what people tend > > > to use when they just have a hard handler (see [1], there's just one > > > driver using it, and it's not even needed, because it's calling > > > devm_request_irq() which adds this flag already) > > It is unclear to me why the current version wants IRQF_COND_ONESHOT in > > one case but not in another. Can't we call devm_request_threaded_irq > > without IRQF_COND_ONESHOT for both cases? > > Hm, I thought this had to do with the automatic hard -> threaded > downgrade happening when RT is enabled, but I fail to see why it > matters, since all irqaction end up with IRQF_ONESHOT in that case > anyway. Honestly, I'm tempted to stay on the safe side, and have > devm_request_irq() called when we just have a hard handler, because I'm > sure there's a reason for this COND_ONESHOT flag. Sounds good. Feel free to add Reviewed-by: Chia-I Wu . FWIW, I think this commit explains the motivation commit c37927a203fa283950f6045602b9f71328ad786c Author: Rafael J. Wysocki Date: Thu Jul 11 12:20:04 2024 +0200 genirq: Set IRQF_COND_ONESHOT in request_irq() The callers of request_irq() don't care about IRQF_ONESHOT because th= ey don't provide threaded handlers, but if they happen to share the IRQ = with the ACPI SCI, which has a threaded handler and sets IRQF_ONESHOT, request_irq() will fail for them due to a flags mismatch. For panthor, my takeaway is we either care about flag mismatch (then we should set IRQF_COND_ONESHOT for the threaded case) or we don't (then we don't need to use devm_request_irq).