linux-kernel - Re: [PATCH 08/18] soc: qcom: ipa: the generic software interface

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Message-ID: <fc8ad575-9ad6-27ab-3255-ef0f41f5b1c5@linaro.org>
Date:   Wed, 15 May 2019 08:32:30 -0500
From:   Alex Elder <elder@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     David Miller <davem@...emloft.net>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        syadagir@...eaurora.org, mjavid@...eaurora.org,
        evgreen@...omium.org, Ben Chan <benchan@...gle.com>,
        Eric Caruso <ejcaruso@...gle.com>, abhishek.esse@...il.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/18] soc: qcom: ipa: the generic software interface

On 5/15/19 5:47 AM, Arnd Bergmann wrote:
> On Sun, May 12, 2019 at 3:25 AM Alex Elder <elder@...aro.org> wrote:
> 
> The per-event interrupt handling seems to be more complex than
> necessary:

I just noticed this message.  I'll take another look at this
whole interrupt control mechanism and will try to streamline
it along the lines of what you describe.

Thanks.

					-Alex

> 
>> +/* Enable or disable an event interrupt */
>> +static void
>> +_gsi_irq_control_event(struct gsi *gsi, u32 evt_ring_id, bool enable)
>> +{
>> +       u32 mask = BIT(evt_ring_id);
>> +       u32 val;
>> +
>> +       if (enable)
>> +               gsi->event_enable_bitmap |= mask;
>> +       else
>> +               gsi->event_enable_bitmap &= ~mask;
>> +
>> +       val = gsi->event_enable_bitmap;
>> +       iowrite32(val, gsi->virt + GSI_CNTXT_SRC_IEOB_IRQ_MSK_OFFSET);
>> +}
>> +
>> +static void gsi_irq_enable_event(struct gsi *gsi, u32 evt_ring_id)
>> +{
>> +       _gsi_irq_control_event(gsi, evt_ring_id, true);
> 
> You maintain a bitmap here of the enabled-state, and have
> to use a spinlock to ensure that the two are in sync.
> 
>> +/* Returns true if the interrupt state (enabled or not) changed */
>> +static bool gsi_channel_intr(struct gsi_channel *channel, bool enable)
>> +{
>> +       u32 evt_ring_id = channel->evt_ring_id;
>> +       struct gsi *gsi = channel->gsi;
>> +       u32 mask = BIT(evt_ring_id);
>> +       unsigned long flags;
>> +       bool different;
>> +       u32 enabled;
>> +
>> +       spin_lock_irqsave(&gsi->spinlock, flags);
>> +
>> +       enabled = gsi->event_enable_bitmap & mask;
>> +       different = enable == !enabled;
>> +
>> +       if (different) {
>> +               if (enabled)
>> +                       gsi_irq_disable_event(channel->gsi, evt_ring_id);
>> +               else
>> +                       gsi_irq_enable_event(channel->gsi, evt_ring_id);
>> +       }
>> +
>> +       spin_unlock_irqrestore(&gsi->spinlock, flags);
>> +
>> +       return different;
>> +}
> 
> This gets called for each active channel, so you repeatedly
> have to get the spinlock and read the irq-enabled state for it.
> 
>> +static void gsi_isr_ieob(struct gsi *gsi)
>> +{
>> +       u32 evt_mask;
>> +
>> +       evt_mask = ioread32(gsi->virt + GSI_CNTXT_SRC_IEOB_IRQ_OFFSET);
>> +       evt_mask &= ioread32(gsi->virt + GSI_CNTXT_SRC_IEOB_IRQ_MSK_OFFSET);
>> +       iowrite32(evt_mask, gsi->virt + GSI_CNTXT_SRC_IEOB_IRQ_CLR_OFFSET);
>> +
>> +       while (evt_mask) {
>> +               u32 evt_ring_id = __ffs(evt_mask);
>> +
>> +               evt_mask ^= BIT(evt_ring_id);
>> +
>> +               gsi_event_handle(gsi, evt_ring_id);
>> +       }
>> +}
> 
> However, you start out by clearing all bits here.
> 
> Why not skip the clearing and and leave the interrupts enabled,
> while moving the GSI_CNTXT_SRC_IEOB_IRQ_CLR_OFFSET
> write (for a single channel that was completed) to the end of
> gsi_channel_poll()?
> 
> Something like
> 
> static void gsi_isr_ieob(struct gsi *gsi)
> {
>       u32 evt_mask;
> 
>       evt_mask = ioread32(gsi->virt + GSI_CNTXT_SRC_IEOB_IRQ_OFFSET);
>       while (evt_mask) {
>                u32 evt_ring_id = __ffs(evt_mask);
>                evt_mask ^= BIT(evt_ring_id);
> 
>                napi_schedule(gsi->evt_ring[evt_ring_id].channel.napi);
>       }
> }
> 
> I also removed the GSI_CNTXT_SRC_IEOB_IRQ_MSK_OFFSET
> read here, as that is probably more expensive than calling napi_schedule()
> for a channel that is already scheduled. Most of the time, I'd expect the
> interrupt to only signal a single channel anyway.
> 
>         Arnd
>