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Mon, 05 Jan 2026 14:16:36 -0800 (PST) Date: Mon, 5 Jan 2026 15:16:33 -0700 From: Mathieu Poirier To: Tzung-Bi Shih Cc: Bjorn Andersson , Matthias Brugger , AngeloGioacchino Del Regno , linux-remoteproc@vger.kernel.org, linux-mediatek@lists.infradead.org Subject: Re: [PATCH] remoteproc: mediatek: Break lock dependency to `prepare_lock` Message-ID: References: <20251229043146.4102967-1-tzungbi@kernel.org> 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: <20251229043146.4102967-1-tzungbi@kernel.org> On Mon, Dec 29, 2025 at 04:31:46AM +0000, Tzung-Bi Shih wrote: > `scp_ipi_send` acquires `prepare_lock` via `clk_prepare_enable` while > the caller often holds `ec_dev->lock` (e.g., `cros_ec_cmd_xfer`). The > reverse dependency exists where `clk_prepare` can trigger operations > that eventually take `ec_dev->lock` (e.g., via sysfs/regulator/genpd). What operation would that be? Please be specific so that I can trace the code. > > Move clock prepare / unprepare operations to remoteproc prepare() / > unprepare() callbacks to break the lock dependency from `ec_dev->lock` > to `prepare_lock`. With the information presented to me, I don't see how doing that changes anything. @prepare_lock is simply held for a longer period of time. Thanks, Mathieu > > This breaks the dependency chain in the lockdep report: > > WARNING: possible circular locking dependency detected > > ... > > the existing dependency chain (in reverse order) is: > > ... > > -> #0 (prepare_lock){+.+.}-{3:3}: > > __lock_acquire > > lock_acquire > > __mutex_lock_common > > mutex_lock_nested > > clk_prepare > > scp_ipi_send [mtk_scp_ipi] > > scp_send_ipi [mtk_scp] > > mtk_rpmsg_send [mtk_rpmsg] > > rpmsg_send [rpmsg_core] > > cros_ec_pkt_xfer_rpmsg [cros_ec_rpmsg] > > Signed-off-by: Tzung-Bi Shih > --- > drivers/remoteproc/mtk_scp.c | 39 +++++++++++++++++++++++--------- > drivers/remoteproc/mtk_scp_ipi.c | 4 ++-- > 2 files changed, 30 insertions(+), 13 deletions(-) > > diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c > index db8fd045468d..98d00bd5200c 100644 > --- a/drivers/remoteproc/mtk_scp.c > +++ b/drivers/remoteproc/mtk_scp.c > @@ -283,7 +283,7 @@ static irqreturn_t scp_irq_handler(int irq, void *priv) > struct mtk_scp *scp = priv; > int ret; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(scp->dev, "failed to enable clocks\n"); > return IRQ_NONE; > @@ -291,7 +291,7 @@ static irqreturn_t scp_irq_handler(int irq, void *priv) > > scp->data->scp_irq_handler(scp); > > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > > return IRQ_HANDLED; > } > @@ -665,7 +665,7 @@ static int scp_load(struct rproc *rproc, const struct firmware *fw) > struct device *dev = scp->dev; > int ret; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(dev, "failed to enable clocks\n"); > return ret; > @@ -680,7 +680,7 @@ static int scp_load(struct rproc *rproc, const struct firmware *fw) > > ret = scp_elf_load_segments(rproc, fw); > leave: > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > > return ret; > } > @@ -691,14 +691,14 @@ static int scp_parse_fw(struct rproc *rproc, const struct firmware *fw) > struct device *dev = scp->dev; > int ret; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(dev, "failed to enable clocks\n"); > return ret; > } > > ret = scp_ipi_init(scp, fw); > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > return ret; > } > > @@ -709,7 +709,7 @@ static int scp_start(struct rproc *rproc) > struct scp_run *run = &scp->run; > int ret; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(dev, "failed to enable clocks\n"); > return ret; > @@ -734,14 +734,14 @@ static int scp_start(struct rproc *rproc) > goto stop; > } > > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > dev_info(dev, "SCP is ready. FW version %s\n", run->fw_ver); > > return 0; > > stop: > scp->data->scp_reset_assert(scp); > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > return ret; > } > > @@ -909,7 +909,7 @@ static int scp_stop(struct rproc *rproc) > struct mtk_scp *scp = rproc->priv; > int ret; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(scp->dev, "failed to enable clocks\n"); > return ret; > @@ -917,12 +917,29 @@ static int scp_stop(struct rproc *rproc) > > scp->data->scp_reset_assert(scp); > scp->data->scp_stop(scp); > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > > return 0; > } > > +static int scp_prepare(struct rproc *rproc) > +{ > + struct mtk_scp *scp = rproc->priv; > + > + return clk_prepare(scp->clk); > +} > + > +static int scp_unprepare(struct rproc *rproc) > +{ > + struct mtk_scp *scp = rproc->priv; > + > + clk_unprepare(scp->clk); > + return 0; > +} > + > static const struct rproc_ops scp_ops = { > + .prepare = scp_prepare, > + .unprepare = scp_unprepare, > .start = scp_start, > .stop = scp_stop, > .load = scp_load, > diff --git a/drivers/remoteproc/mtk_scp_ipi.c b/drivers/remoteproc/mtk_scp_ipi.c > index c068227e251e..7a37e273b3af 100644 > --- a/drivers/remoteproc/mtk_scp_ipi.c > +++ b/drivers/remoteproc/mtk_scp_ipi.c > @@ -171,7 +171,7 @@ int scp_ipi_send(struct mtk_scp *scp, u32 id, void *buf, unsigned int len, > WARN_ON(len > scp_sizes->ipi_share_buffer_size) || WARN_ON(!buf)) > return -EINVAL; > > - ret = clk_prepare_enable(scp->clk); > + ret = clk_enable(scp->clk); > if (ret) { > dev_err(scp->dev, "failed to enable clock\n"); > return ret; > @@ -211,7 +211,7 @@ int scp_ipi_send(struct mtk_scp *scp, u32 id, void *buf, unsigned int len, > > unlock_mutex: > mutex_unlock(&scp->send_lock); > - clk_disable_unprepare(scp->clk); > + clk_disable(scp->clk); > > return ret; > } > -- > 2.52.0.351.gbe84eed79e-goog >