From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> To: Sean Anderson <sean.anderson@linux.dev> Cc: Michal Simek <michal.simek@amd.com>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Vinod Koul <vkoul@kernel.org>, dmaengine@vger.kernel.org Subject: Re: [PATCH 2/3] dma: xilinx_dpdma: Remove unnecessary use of irqsave/restore Date: Wed, 27 Mar 2024 14:27:08 +0200 [thread overview] Message-ID: <0652c82f-b0a2-4881-ac51-38399b180ad4@ideasonboard.com> (raw) In-Reply-To: <20240308210034.3634938-3-sean.anderson@linux.dev> Hi, On 08/03/2024 23:00, Sean Anderson wrote: > xilinx_dpdma_chan_done_irq and xilinx_dpdma_chan_vsync_irq are always > called with IRQs disabled from xilinx_dpdma_irq_handler. Therefore we > don't need to save/restore the IRQ flags. I think this is fine, but a few thoughts: - Is spin_lock clearly faster than the irqsave variant, or is this a pointless optimization? It's safer to just use irqsave variant, instead of making sure the code is always called from the expected contexts. - Is this style documented/recommended anywhere? Going through docs, I only found docs telling to use irqsave when mixing irq and non-irq contexts. - Does this cause issues on PREEMPT_RT? Tomi > Signed-off-by: Sean Anderson <sean.anderson@linux.dev> > --- > > drivers/dma/xilinx/xilinx_dpdma.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c > index eb0637d90342..36bd4825d389 100644 > --- a/drivers/dma/xilinx/xilinx_dpdma.c > +++ b/drivers/dma/xilinx/xilinx_dpdma.c > @@ -1043,9 +1043,8 @@ static int xilinx_dpdma_chan_stop(struct xilinx_dpdma_chan *chan) > static void xilinx_dpdma_chan_done_irq(struct xilinx_dpdma_chan *chan) > { > struct xilinx_dpdma_tx_desc *active; > - unsigned long flags; > > - spin_lock_irqsave(&chan->lock, flags); > + spin_lock(&chan->lock); > > xilinx_dpdma_debugfs_desc_done_irq(chan); > > @@ -1057,7 +1056,7 @@ static void xilinx_dpdma_chan_done_irq(struct xilinx_dpdma_chan *chan) > "chan%u: DONE IRQ with no active descriptor!\n", > chan->id); > > - spin_unlock_irqrestore(&chan->lock, flags); > + spin_unlock(&chan->lock); > } > > /** > @@ -1072,10 +1071,9 @@ static void xilinx_dpdma_chan_vsync_irq(struct xilinx_dpdma_chan *chan) > { > struct xilinx_dpdma_tx_desc *pending; > struct xilinx_dpdma_sw_desc *sw_desc; > - unsigned long flags; > u32 desc_id; > > - spin_lock_irqsave(&chan->lock, flags); > + spin_lock(&chan->lock); > > pending = chan->desc.pending; > if (!chan->running || !pending) > @@ -1108,7 +1106,7 @@ static void xilinx_dpdma_chan_vsync_irq(struct xilinx_dpdma_chan *chan) > spin_unlock(&chan->vchan.lock); > > out: > - spin_unlock_irqrestore(&chan->lock, flags); > + spin_unlock(&chan->lock); > } > > /**
WARNING: multiple messages have this Message-ID (diff)
From: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> To: Sean Anderson <sean.anderson@linux.dev> Cc: Michal Simek <michal.simek@amd.com>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Laurent Pinchart <laurent.pinchart@ideasonboard.com>, Vinod Koul <vkoul@kernel.org>, dmaengine@vger.kernel.org Subject: Re: [PATCH 2/3] dma: xilinx_dpdma: Remove unnecessary use of irqsave/restore Date: Wed, 27 Mar 2024 14:27:08 +0200 [thread overview] Message-ID: <0652c82f-b0a2-4881-ac51-38399b180ad4@ideasonboard.com> (raw) In-Reply-To: <20240308210034.3634938-3-sean.anderson@linux.dev> Hi, On 08/03/2024 23:00, Sean Anderson wrote: > xilinx_dpdma_chan_done_irq and xilinx_dpdma_chan_vsync_irq are always > called with IRQs disabled from xilinx_dpdma_irq_handler. Therefore we > don't need to save/restore the IRQ flags. I think this is fine, but a few thoughts: - Is spin_lock clearly faster than the irqsave variant, or is this a pointless optimization? It's safer to just use irqsave variant, instead of making sure the code is always called from the expected contexts. - Is this style documented/recommended anywhere? Going through docs, I only found docs telling to use irqsave when mixing irq and non-irq contexts. - Does this cause issues on PREEMPT_RT? Tomi > Signed-off-by: Sean Anderson <sean.anderson@linux.dev> > --- > > drivers/dma/xilinx/xilinx_dpdma.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/drivers/dma/xilinx/xilinx_dpdma.c b/drivers/dma/xilinx/xilinx_dpdma.c > index eb0637d90342..36bd4825d389 100644 > --- a/drivers/dma/xilinx/xilinx_dpdma.c > +++ b/drivers/dma/xilinx/xilinx_dpdma.c > @@ -1043,9 +1043,8 @@ static int xilinx_dpdma_chan_stop(struct xilinx_dpdma_chan *chan) > static void xilinx_dpdma_chan_done_irq(struct xilinx_dpdma_chan *chan) > { > struct xilinx_dpdma_tx_desc *active; > - unsigned long flags; > > - spin_lock_irqsave(&chan->lock, flags); > + spin_lock(&chan->lock); > > xilinx_dpdma_debugfs_desc_done_irq(chan); > > @@ -1057,7 +1056,7 @@ static void xilinx_dpdma_chan_done_irq(struct xilinx_dpdma_chan *chan) > "chan%u: DONE IRQ with no active descriptor!\n", > chan->id); > > - spin_unlock_irqrestore(&chan->lock, flags); > + spin_unlock(&chan->lock); > } > > /** > @@ -1072,10 +1071,9 @@ static void xilinx_dpdma_chan_vsync_irq(struct xilinx_dpdma_chan *chan) > { > struct xilinx_dpdma_tx_desc *pending; > struct xilinx_dpdma_sw_desc *sw_desc; > - unsigned long flags; > u32 desc_id; > > - spin_lock_irqsave(&chan->lock, flags); > + spin_lock(&chan->lock); > > pending = chan->desc.pending; > if (!chan->running || !pending) > @@ -1108,7 +1106,7 @@ static void xilinx_dpdma_chan_vsync_irq(struct xilinx_dpdma_chan *chan) > spin_unlock(&chan->vchan.lock); > > out: > - spin_unlock_irqrestore(&chan->lock, flags); > + spin_unlock(&chan->lock); > } > > /** _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-03-27 12:27 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-03-08 21:00 [PATCH 0/3] dma: xilinx_dpdma: Fix locking Sean Anderson 2024-03-08 21:00 ` Sean Anderson 2024-03-08 21:00 ` [PATCH 1/3] " Sean Anderson 2024-03-08 21:00 ` Sean Anderson 2024-03-27 11:57 ` Tomi Valkeinen 2024-03-27 11:57 ` Tomi Valkeinen 2024-03-08 21:00 ` [PATCH 2/3] dma: xilinx_dpdma: Remove unnecessary use of irqsave/restore Sean Anderson 2024-03-08 21:00 ` Sean Anderson 2024-03-27 12:27 ` Tomi Valkeinen [this message] 2024-03-27 12:27 ` Tomi Valkeinen 2024-03-28 15:00 ` Sean Anderson 2024-03-28 15:00 ` Sean Anderson 2024-03-28 16:37 ` Tomi Valkeinen 2024-03-28 16:37 ` Tomi Valkeinen 2024-03-08 21:00 ` [PATCH 3/3] dma: Add lockdep asserts to virt-dma Sean Anderson 2024-03-08 21:00 ` Sean Anderson 2024-03-27 12:29 ` Tomi Valkeinen 2024-03-27 12:29 ` Tomi Valkeinen 2024-04-07 16:38 ` [PATCH 0/3] dma: xilinx_dpdma: Fix locking Vinod Koul 2024-04-07 16:38 ` Vinod Koul
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