Messages in this thread | | | Date | Wed, 27 Mar 2024 14:27:08 +0200 | Subject | Re: [PATCH 2/3] dma: xilinx_dpdma: Remove unnecessary use of irqsave/restore | From | Tomi Valkeinen <> |
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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); > } > > /**
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