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SubjectRe: [PATCH net-next 9/9] net: ipa: don't disable NAPI in suspend
On Fri, Jan 29, 2021 at 3:29 PM Alex Elder <elder@linaro.org> wrote:
>
> The channel stop and suspend paths both call __gsi_channel_stop(),
> which quiesces channel activity, disables NAPI, and (on other than
> SDM845) stops the channel. Similarly, the start and resume paths
> share __gsi_channel_start(), which starts the channel and re-enables
> NAPI again.
>
> Disabling NAPI should be done when stopping a channel, but this
> should *not* be done when suspending. It's not necessary in the
> suspend path anyway, because the stopped channel (or suspended
> endpoint on SDM845) will not cause interrupts to schedule NAPI,
> and gsi_channel_trans_quiesce() won't return until there are no
> more transactions to process in the NAPI polling loop.

But why is it incorrect to do so?

From a quick look, virtio-net disables on both remove and freeze, for instance.

> Instead, enable NAPI in gsi_channel_start(), when the completion
> interrupt is first enabled. Disable it again in gsi_channel_stop(),
> when finally disabling the interrupt.
>
> Add a call to napi_synchronize() to __gsi_channel_stop(), to ensure
> NAPI polling is done before moving on.
>
> Signed-off-by: Alex Elder <elder@linaro.org>
> ---
=
> @@ -894,12 +894,16 @@ int gsi_channel_start(struct gsi *gsi, u32 channel_id)
> struct gsi_channel *channel = &gsi->channel[channel_id];
> int ret;
>
> - /* Enable the completion interrupt */
> + /* Enable NAPI and the completion interrupt */
> + napi_enable(&channel->napi);
> gsi_irq_ieob_enable_one(gsi, channel->evt_ring_id);
>
> ret = __gsi_channel_start(channel, true);
> - if (ret)
> - gsi_irq_ieob_disable_one(gsi, channel->evt_ring_id);
> + if (!ret)
> + return 0;
> +
> + gsi_irq_ieob_disable_one(gsi, channel->evt_ring_id);
> + napi_disable(&channel->napi);
>
> return ret;
> }

subjective, but easier to parse when the normal control flow is linear
and the error path takes a branch (or goto, if reused).

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