From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2DF4122D7B5 for ; Mon, 15 Dec 2025 01:04:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765760690; cv=none; b=NqW5Gpe8Uo2LL/uipcdOUIuIbTP25sibnuOrY91bZL+MfP4Vi9ju4Fs2O58PPAYsv9pxUxAIr7ROccJZxnEefZ3J1wSahxvuh9nS/mEO5Ld/VTzWoaN7ZYId5ygiHgRr+e9ZzfpLO22VZhF+ZqFJdaK95Eh05+6LfwjwIm1Lkqk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765760690; c=relaxed/simple; bh=XWyq5s6tv/TqDiKny8B7IeTrEaEsHnviazHxisaV9Ys=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OskqwGXP3MxU2WFF+Ht5kVPasvpMvVk0ZtI8lNuzbIb21vGvvMw1zJ5JxmTAfHWIHgPFQnfhgvw5elvm1mO6Rml0YwNccQausi2QKUDRRKwyCryY4fu6j2vNUoQP2ErEa0/W4zNJ9SqKCmVORZ9k8bhDXVAeyKwrydfwLdE5xkg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linaro.org; spf=pass smtp.mailfrom=linaro.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b=hJ70lEC3; arc=none smtp.client-ip=209.85.214.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linaro.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linaro.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="hJ70lEC3" Received: by mail-pl1-f179.google.com with SMTP id d9443c01a7336-29efd139227so35363805ad.1 for ; Sun, 14 Dec 2025 17:04:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1765760687; x=1766365487; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=inC+Wy9jzavRGBSwjZxV0qHxl3oyLnDwyagmXqiYjYQ=; b=hJ70lEC3isL6tko28fuPx3vWiBF388Pmw5MXDqqDDJu37dRkRSFgxLdIPG0ou9J1uy YbBOxMPg7YuZyUfS9y24r2zRRoqDC17etO04KAbVUWrj5QwsJ1OD7In4BRVxc2Aq2ddN BvddHxI2H58opwZKn+a9gzjGhD9Xnt3h5CB+f1C2HdfHcDFGPa+x9OhbePuyxy5Lgrzd vhNFzfweZSDEgbMrT3t69uYWfBv1sgtFrHKAbrxi1OupCwXMoZG6QZCpvqoaNe3D/0SN Mmd+E5m7/PM6I77z7epRCTkiLDq0/o7ndtSs+as+AAd29OZT+fTHeBFu/ygdKR7ZXKwU Y/oQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765760687; x=1766365487; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=inC+Wy9jzavRGBSwjZxV0qHxl3oyLnDwyagmXqiYjYQ=; b=qxUi6UMyozo1B2v3kObMo+3xpmz3oP6YSwLAj+FappuWLLsOVTba95vKrXWxqItP23 hNcNZ6sQz6zrF3gmRLHuigL0ztdqUdg2uFhz0GhaRCz3OhVDfZx77vz1ZhsdBWTwux/C Ux8+QSSDbHO6hSJ8CBoUWl+D4iULV01A07FE1CEaiYDug1nQYHBULobR5Ob7HwtoaXrk yn5A3YUa3G5jH59uB8BNSVYfjBpazxNnzaIXOASSSwuXNH7GOQKWTM/KGES+BSkrfG9f bgvCEK1pAaBDiEUvg3O06tmK0iyq1kV065I5MB8kZsBMFsRCdisX1U4kqjYfxvfs6L2y KXFw== X-Gm-Message-State: AOJu0YyyMTsjbmOK1L/l6p0093ZFEs4JW9VS4tcQElJ+VwAKAu2YT086 0kdBrAaAH6N8xNPnzLbyas1zLB0B1+kXJuLBV/zmN19uNWPliFPt2IxnAwVxR6hkf2Q= X-Gm-Gg: AY/fxX7usiLOYy87gLDCRxVKJq99iBu21VBKEFvNPJNuQ/9N/SBgWDQ2CG71axcyVrx ttUDe8rManC9H1VbHxgcnLatNU/Z4XFxpSwxJWuFdd3ebLiFE632HD9kntir/YcJeM8g4l5rTg6 kUPwAooOu7jh7/1KJBcnoGZt5JOYpXmkuJJ0cPJSrw5gP2CjBNZZdYHUtOT9tb+zAyVjQgHnJkH /4BvN6W1RGiMwKlXpYiNwFyDkdWJM/ymLB3rPzlmmsp1D69KaI/Ih+0nWg4jvvyv/6RLrwb+uxg HdwZRI1tI8SM50nAhigbSuvlTLp36nbKKcZw386m4uylYQskrAOJ7zcFFuzMs1xyYBkS/GgnNmp N+SMOrGYNhLXOX7ph9BPJlgftHbbxIFdZlCft8E2Ujbz0XUYigpihjuVxxIh/wlGL+ihhU7drV6 9Iszezr7CbCbxfp4Qxm0vH34DIL7mFGZzKdAyRWn2+ow== X-Google-Smtp-Source: AGHT+IH780U+szUHUNQS1YjqiBuVr0+NPVsL48001MXGp8vaAOzfLNXng9apn4f0AJiTSkwsjQO5dg== X-Received: by 2002:a17:903:32cd:b0:29e:97a1:76bc with SMTP id d9443c01a7336-29f23b5ecf4mr93977595ad.21.1765760687185; Sun, 14 Dec 2025 17:04:47 -0800 (PST) Received: from p14s (p7838222-ipoefx.ipoe.ocn.ne.jp. [123.225.39.221]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a09afe20e5sm46224665ad.26.2025.12.14.17.04.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 14 Dec 2025 17:04:46 -0800 (PST) Date: Sun, 14 Dec 2025 18:04:43 -0700 From: Mathieu Poirier To: patrick.oppenlander@gmail.com Cc: linux-remoteproc@vger.kernel.org, andersson@kernel.org Subject: Re: [PATCH] rpmsg: virtio: EPOLLOUT support Message-ID: References: <20251022032817.320378-1-patrick.oppenlander@gmail.com> Precedence: bulk X-Mailing-List: linux-remoteproc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251022032817.320378-1-patrick.oppenlander@gmail.com> On Wed, Oct 22, 2025 at 02:28:17PM +1100, patrick.oppenlander@gmail.com wrote: > From: Patrick Oppenlander > > Previously, polling an rpmsg endpoint (e.g. /dev/ttyRPMSGx) would > generate EPOLLIN events but no EPOLLOUT events. > > Unfortunately, poll support means that we can no longer disable > tx-complete interrupts as there is no way to know whether a poller is > waiting in sendq, so we always need notifications. > > Signed-off-by: Patrick Oppenlander > --- > drivers/rpmsg/virtio_rpmsg_bus.c | 101 ++++++++++--------------------- > 1 file changed, 32 insertions(+), 69 deletions(-) > As we previously agreed, I have added this patch to my tree under the condition it doesn't break anything. Let's see how things go. Thanks, Mathieu > diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c > index 484890b4a6a74..79d983055b4d6 100644 > --- a/drivers/rpmsg/virtio_rpmsg_bus.c > +++ b/drivers/rpmsg/virtio_rpmsg_bus.c > @@ -41,13 +41,12 @@ > * @buf_size: size of one rx or tx buffer > * @last_sbuf: index of last tx buffer used > * @bufs_dma: dma base addr of the buffers > - * @tx_lock: protects svq, sbufs and sleepers, to allow concurrent senders. > + * @tx_lock: protects svq and sbufs, to allow concurrent senders. > * sending a message might require waking up a dozing remote > * processor, which involves sleeping, hence the mutex. > * @endpoints: idr of local endpoints, allows fast retrieval > * @endpoints_lock: lock of the endpoints set > * @sendq: wait queue of sending contexts waiting for a tx buffers > - * @sleepers: number of senders that are waiting for a tx buffer > * > * This structure stores the rpmsg state of a given virtio remote processor > * device (there might be several virtio proc devices for each physical > @@ -65,7 +64,6 @@ struct virtproc_info { > struct idr endpoints; > struct mutex endpoints_lock; > wait_queue_head_t sendq; > - atomic_t sleepers; > }; > > /* The feature bitmap for virtio rpmsg */ > @@ -144,6 +142,8 @@ static int virtio_rpmsg_sendto(struct rpmsg_endpoint *ept, void *data, int len, > static int virtio_rpmsg_trysend(struct rpmsg_endpoint *ept, void *data, int len); > static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data, > int len, u32 dst); > +static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp, > + poll_table *wait); > static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept); > static struct rpmsg_device *__rpmsg_create_channel(struct virtproc_info *vrp, > struct rpmsg_channel_info *chinfo); > @@ -154,6 +154,7 @@ static const struct rpmsg_endpoint_ops virtio_endpoint_ops = { > .sendto = virtio_rpmsg_sendto, > .trysend = virtio_rpmsg_trysend, > .trysendto = virtio_rpmsg_trysendto, > + .poll = virtio_rpmsg_poll, > .get_mtu = virtio_rpmsg_get_mtu, > }; > > @@ -436,7 +437,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp) > unsigned int len; > void *ret; > > - /* support multiple concurrent senders */ > mutex_lock(&vrp->tx_lock); > > /* > @@ -454,62 +454,6 @@ static void *get_a_tx_buf(struct virtproc_info *vrp) > return ret; > } > > -/** > - * rpmsg_upref_sleepers() - enable "tx-complete" interrupts, if needed > - * @vrp: virtual remote processor state > - * > - * This function is called before a sender is blocked, waiting for > - * a tx buffer to become available. > - * > - * If we already have blocking senders, this function merely increases > - * the "sleepers" reference count, and exits. > - * > - * Otherwise, if this is the first sender to block, we also enable > - * virtio's tx callbacks, so we'd be immediately notified when a tx > - * buffer is consumed (we rely on virtio's tx callback in order > - * to wake up sleeping senders as soon as a tx buffer is used by the > - * remote processor). > - */ > -static void rpmsg_upref_sleepers(struct virtproc_info *vrp) > -{ > - /* support multiple concurrent senders */ > - mutex_lock(&vrp->tx_lock); > - > - /* are we the first sleeping context waiting for tx buffers ? */ > - if (atomic_inc_return(&vrp->sleepers) == 1) > - /* enable "tx-complete" interrupts before dozing off */ > - virtqueue_enable_cb(vrp->svq); > - > - mutex_unlock(&vrp->tx_lock); > -} > - > -/** > - * rpmsg_downref_sleepers() - disable "tx-complete" interrupts, if needed > - * @vrp: virtual remote processor state > - * > - * This function is called after a sender, that waited for a tx buffer > - * to become available, is unblocked. > - * > - * If we still have blocking senders, this function merely decreases > - * the "sleepers" reference count, and exits. > - * > - * Otherwise, if there are no more blocking senders, we also disable > - * virtio's tx callbacks, to avoid the overhead incurred with handling > - * those (now redundant) interrupts. > - */ > -static void rpmsg_downref_sleepers(struct virtproc_info *vrp) > -{ > - /* support multiple concurrent senders */ > - mutex_lock(&vrp->tx_lock); > - > - /* are we the last sleeping context waiting for tx buffers ? */ > - if (atomic_dec_and_test(&vrp->sleepers)) > - /* disable "tx-complete" interrupts */ > - virtqueue_disable_cb(vrp->svq); > - > - mutex_unlock(&vrp->tx_lock); > -} > - > /** > * rpmsg_send_offchannel_raw() - send a message across to the remote processor > * @rpdev: the rpmsg channel > @@ -582,9 +526,6 @@ static int rpmsg_send_offchannel_raw(struct rpmsg_device *rpdev, > > /* no free buffer ? wait for one (but bail after 15 seconds) */ > while (!msg) { > - /* enable "tx-complete" interrupts, if not already enabled */ > - rpmsg_upref_sleepers(vrp); > - > /* > * sleep until a free buffer is available or 15 secs elapse. > * the timeout period is not configurable because there's > @@ -595,9 +536,6 @@ static int rpmsg_send_offchannel_raw(struct rpmsg_device *rpdev, > (msg = get_a_tx_buf(vrp)), > msecs_to_jiffies(15000)); > > - /* disable "tx-complete" interrupts if we're the last sleeper */ > - rpmsg_downref_sleepers(vrp); > - > /* timeout ? */ > if (!err) { > dev_err(dev, "timeout waiting for a tx buffer\n"); > @@ -676,6 +614,34 @@ static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data, > return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false); > } > > +static __poll_t virtio_rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp, > + poll_table *wait) > +{ > + struct rpmsg_device *rpdev = ept->rpdev; > + struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev); > + struct virtproc_info *vrp = vch->vrp; > + __poll_t mask = 0; > + > + poll_wait(filp, &vrp->sendq, wait); > + > + /* support multiple concurrent senders */ > + mutex_lock(&vrp->tx_lock); > + > + /* > + * check for a free buffer, either: > + * - we haven't used all of the available transmit buffers (half of the > + * allocated buffers are used for transmit, hence num_bufs / 2), or, > + * - we ask the virtqueue if there's a buffer available > + */ > + if (vrp->last_sbuf < vrp->num_bufs / 2 || > + !virtqueue_enable_cb(vrp->svq)) > + mask |= EPOLLOUT; > + > + mutex_unlock(&vrp->tx_lock); > + > + return mask; > +} > + > static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept) > { > struct rpmsg_device *rpdev = ept->rpdev; > @@ -922,9 +888,6 @@ static int rpmsg_probe(struct virtio_device *vdev) > WARN_ON(err); /* sanity check; this can't really happen */ > } > > - /* suppress "tx-complete" interrupts */ > - virtqueue_disable_cb(vrp->svq); > - > vdev->priv = vrp; > > rpdev_ctrl = rpmsg_virtio_add_ctrl_dev(vdev); > -- > 2.51.1.dirty >