From: Arnd Bergmann <arnd@arndb.de>
To: Alex Elder <elder@linaro.org>
Cc: David Miller <davem@davemloft.net>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Ilias Apalodimas <ilias.apalodimas@linaro.org>,
syadagir@codeaurora.org, mjavid@codeaurora.org,
evgreen@chromium.org, Ben Chan <benchan@google.com>,
Eric Caruso <ejcaruso@google.com>,
abhishek.esse@gmail.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 08/18] soc: qcom: ipa: the generic software interface
Date: Wed, 15 May 2019 14:40:16 +0200 [thread overview]
Message-ID: <CAK8P3a3RCHF0UyKunaoCNvEd0X9EiD62PPfnfGxKG1L95Jz7dA@mail.gmail.com> (raw)
In-Reply-To: <72869c32-c2c5-54f9-10d9-8c0ed9f6300d@linaro.org>
On Wed, May 15, 2019 at 2:13 PM Alex Elder <elder@linaro.org> wrote:
> On 5/15/19 2:21 AM, Arnd Bergmann wrote:
> >> +/* Wait for all transaction activity on a channel to complete */
> >> +void gsi_channel_trans_quiesce(struct gsi *gsi, u32 channel_id)
> >> +{
> >> + struct gsi_channel *channel = &gsi->channel[channel_id];
> >> + struct gsi_trans_info *trans_info;
> >> + struct gsi_trans *trans = NULL;
> >> + struct gsi_evt_ring *evt_ring;
> >> + struct list_head *list;
> >> + unsigned long flags;
> >> +
> >> + trans_info = &channel->trans_info;
> >> + evt_ring = &channel->gsi->evt_ring[channel->evt_ring_id];
> >> +
> >> + spin_lock_irqsave(&evt_ring->ring.spinlock, flags);
> >> +
> >> + /* Find the last list to which a transaction was added */
> >> + if (!list_empty(&trans_info->alloc))
> >> + list = &trans_info->alloc;
> >> + else if (!list_empty(&trans_info->pending))
> >> + list = &trans_info->pending;
> >> + else if (!list_empty(&trans_info->complete))
> >> + list = &trans_info->complete;
> >> + else if (!list_empty(&trans_info->polled))
> >> + list = &trans_info->polled;
> >> + else
> >> + list = NULL;
> >> +
> >> + if (list) {
> >> + struct gsi_trans *trans;
> >> +
> >> + /* The last entry on this list is the last one allocated.
> >> + * Grab a reference so we can wait for it.
> >> + */
> >> + trans = list_last_entry(list, struct gsi_trans, links);
> >> + refcount_inc(&trans->refcount);
> >> + }
> >> +
> >> + spin_lock_irqsave(&evt_ring->ring.spinlock, flags);
> >> +
> >> + /* If there is one, wait for it to complete */
> >> + if (trans) {
> >> + wait_for_completion(&trans->completion);
> >
> > Since you are waiting here, you clearly can't be called
> > from interrupt context, or with interrupts disabled, so it's
> > clearer to use spin_lock_irq() instead of spin_lock_irqsave().
> >
> > I generally try to avoid the _irqsave versions altogether, unless
> > it is really needed for a function that is called both from
> > irq-disabled and irq-enabled context.
>
> OK. And I appreciate what your saying here because I do prefer
> code that communicates more about the context in ways like
> you describe.
Right, also reading the status of the irq-enable flag can be
expensive on some CPUs, so spin_lock_irqsave() ends up
much more slower than spin_lock() or spin_lock_irq(). Not sure
if it makes a huge difference on this particular platform, but
it's better not to have to worry about it.
Arnd
next prev parent reply other threads:[~2019-05-15 12:40 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-12 1:24 [PATCH 00/18] net: introduce Qualcomm IPA driver Alex Elder
2019-05-12 1:24 ` [PATCH 01/18] bitfield.h: add FIELD_MAX() and field_max() Alex Elder
2019-05-12 6:33 ` Kalle Valo
2019-05-12 12:18 ` Alex Elder
2019-05-12 19:30 ` Johannes Berg
2019-05-12 1:24 ` [PATCH 02/18] soc: qcom: create "include/soc/qcom/rmnet.h" Alex Elder
2019-05-12 2:34 ` Joe Perches
2019-05-12 12:15 ` Alex Elder
2019-05-15 6:59 ` Arnd Bergmann
2019-05-15 12:03 ` Alex Elder
2019-05-16 1:09 ` Subash Abhinov Kasiviswanathan
2019-05-17 17:27 ` Alex Elder
2019-05-17 18:08 ` Subash Abhinov Kasiviswanathan
2019-05-19 17:37 ` Alex Elder
2019-05-12 1:24 ` [PATCH 03/18] dt-bindings: soc: qcom: add IPA bindings Alex Elder
2019-05-15 7:03 ` Arnd Bergmann
2019-05-15 12:04 ` Alex Elder
2019-05-15 16:50 ` Rob Herring
2019-05-15 17:05 ` Alex Elder
2019-05-12 1:24 ` [PATCH 04/18] soc: qcom: ipa: main code Alex Elder
2019-05-12 1:24 ` [PATCH 05/18] soc: qcom: ipa: configuration data Alex Elder
2019-05-12 1:24 ` [PATCH 06/18] soc: qcom: ipa: clocking, interrupts, and memory Alex Elder
2019-05-12 1:24 ` [PATCH 07/18] soc: qcom: ipa: GSI headers Alex Elder
2019-05-12 1:24 ` [PATCH 08/18] soc: qcom: ipa: the generic software interface Alex Elder
2019-05-15 7:21 ` Arnd Bergmann
2019-05-15 12:13 ` Alex Elder
2019-05-15 12:40 ` Arnd Bergmann [this message]
2019-05-15 10:47 ` Arnd Bergmann
2019-05-15 13:32 ` Alex Elder
2019-05-15 19:37 ` Arnd Bergmann
2019-05-12 1:24 ` [PATCH 09/18] soc: qcom: ipa: GSI transactions Alex Elder
2019-05-15 7:34 ` Arnd Bergmann
2019-05-15 12:25 ` Alex Elder
2019-05-15 20:50 ` Arnd Bergmann
2019-05-17 18:08 ` Alex Elder
2019-05-17 18:33 ` Arnd Bergmann
2019-05-17 18:44 ` Alex Elder
2019-05-19 17:11 ` Alex Elder
2019-05-20 9:25 ` Arnd Bergmann
2019-05-20 12:50 ` Alex Elder
2019-05-20 14:43 ` Arnd Bergmann
2019-05-20 14:44 ` Alex Elder
2019-05-20 16:34 ` Evan Green
2019-05-20 16:50 ` Alex Elder
2019-05-20 17:36 ` Evan Green
2019-05-12 1:25 ` [PATCH 10/18] soc: qcom: ipa: IPA interface to GSI Alex Elder
2019-05-12 1:25 ` [PATCH 11/18] soc: qcom: ipa: IPA endpoints Alex Elder
2019-05-12 1:25 ` [PATCH 12/18] soc: qcom: ipa: immediate commands Alex Elder
2019-05-15 8:16 ` Arnd Bergmann
2019-05-15 12:35 ` Alex Elder
2019-05-18 0:34 ` Alex Elder
2019-05-20 14:50 ` Arnd Bergmann
2019-05-20 14:55 ` Alex Elder
2019-05-20 17:35 ` Christoph Hellwig
2019-05-12 1:25 ` [PATCH 13/18] soc: qcom: ipa: IPA network device and microcontroller Alex Elder
2019-05-15 8:21 ` Arnd Bergmann
2019-05-15 12:46 ` Alex Elder
2019-05-12 1:25 ` [PATCH 14/18] soc: qcom: ipa: AP/modem communications Alex Elder
2019-05-12 1:25 ` [PATCH 15/18] soc: qcom: ipa: support build of IPA code Alex Elder
2019-05-12 1:25 ` [PATCH 16/18] MAINTAINERS: add entry for the Qualcomm IPA driver Alex Elder
2019-05-12 1:25 ` [PATCH 17/18] arm64: dts: sdm845: add IPA information Alex Elder
2019-05-12 1:25 ` [PATCH 18/18] arm64: defconfig: enable build of IPA code Alex Elder
2019-05-15 8:23 ` Arnd Bergmann
2019-05-15 12:49 ` Alex Elder
2019-05-15 12:37 ` [PATCH 00/18] net: introduce Qualcomm IPA driver Arnd Bergmann
2019-05-15 12:52 ` Alex Elder
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