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Message-ID: <20240809174043.0000011a.zhiw@nvidia.com>
Date: Fri, 9 Aug 2024 17:40:43 +0300
From: Zhi Wang <zhiw@...dia.com>
To: <alejandro.lucero-palau@....com>
CC: <linux-cxl@...r.kernel.org>, <netdev@...r.kernel.org>,
<dan.j.williams@...el.com>, <martin.habets@...inx.com>,
<edward.cree@....com>, <davem@...emloft.net>, <kuba@...nel.org>,
<pabeni@...hat.com>, <edumazet@...gle.com>, <richard.hughes@....com>,
Alejandro Lucero <alucerop@....com>, <targupta@...dia.com>
Subject: Re: [PATCH v2 08/15] cxl: indicate probe deferral
On Mon, 15 Jul 2024 18:28:28 +0100
<alejandro.lucero-palau@....com> wrote:
Another spell check is spotted besides others review threads. Will
circle back with more comments once checking the users of the APIs.
> From: Alejandro Lucero <alucerop@....com>
>
> The first stop for a CXL accelerator driver that wants to establish
> new CXL.mem regions is to register a 'struct cxl_memdev. That kicks
> off cxl_mem_probe() to enumerate all 'struct cxl_port' instances in
> the topology up to the root.
>
> If the root driver has not attached yet the expectation is that the
> driver waits until that link is established. The common cxl_pci_driver
> has reason to keep the 'struct cxl_memdev' device attached to the bus
> until the root driver attaches. An accelerator may want to instead
> defer probing until CXL resources can be acquired.
>
> Use the @endpoint attribute of a 'struct cxl_memdev' to convey when
> accelerator driver probing should be defferred vs failed. Provide that
^deferred
> indication via a new cxl_acquire_endpoint() API that can retrieve the
> probe status of the memdev.
>
> The first consumer of this API is a test driver that excercises the
> CXL Type-2 flow.
>
> Based on
> https://lore.kernel.org/linux-cxl/168592149709.1948938.8663425987110396027.stgit@dwillia2-xfh.jf.intel.com/T/#m18497367d2ae38f88e94c06369eaa83fa23e92b2
>
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> Co-developed-by: Dan Williams <dan.j.williams@...el.com>
> ---
> drivers/cxl/core/memdev.c | 41
> ++++++++++++++++++++++++++++++ drivers/cxl/core/port.c |
> 2 +- drivers/cxl/mem.c | 7 +++--
> drivers/net/ethernet/sfc/efx_cxl.c | 10 +++++++-
> include/linux/cxl_accel_mem.h | 3 +++
> 5 files changed, 59 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index b902948b121f..d51c8bfb32e3 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -1137,6 +1137,47 @@ struct cxl_memdev *devm_cxl_add_memdev(struct
> device *host, }
> EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, CXL);
>
> +/*
> + * Try to get a locked reference on a memdev's CXL port topology
> + * connection. Be careful to observe when cxl_mem_probe() has
> deposited
> + * a probe deferral awaiting the arrival of the CXL root driver
> +*/
> +struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd)
> +{
> + struct cxl_port *endpoint;
> + int rc = -ENXIO;
> +
> + device_lock(&cxlmd->dev);
> + endpoint = cxlmd->endpoint;
> + if (!endpoint)
> + goto err;
> +
> + if (IS_ERR(endpoint)) {
> + rc = PTR_ERR(endpoint);
> + goto err;
> + }
> +
> + device_lock(&endpoint->dev);
> + if (!endpoint->dev.driver)
> + goto err_endpoint;
> +
> + return endpoint;
> +
> +err_endpoint:
> + device_unlock(&endpoint->dev);
> +err:
> + device_unlock(&cxlmd->dev);
> + return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_NS(cxl_acquire_endpoint, CXL);
> +
> +void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port
> *endpoint) +{
> + device_unlock(&endpoint->dev);
> + device_unlock(&cxlmd->dev);
> +}
> +EXPORT_SYMBOL_NS(cxl_release_endpoint, CXL);
> +
> static void sanitize_teardown_notifier(void *data)
> {
> struct cxl_memdev_state *mds = data;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index d66c6349ed2d..3c6b896c5f65 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1553,7 +1553,7 @@ static int add_port_attach_ep(struct cxl_memdev
> *cxlmd, */
> dev_dbg(&cxlmd->dev, "%s is a root dport\n",
> dev_name(dport_dev));
> - return -ENXIO;
> + return -EPROBE_DEFER;
> }
>
> parent_port = find_cxl_port(dparent, &parent_dport);
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index f76af75a87b7..383a6f4829d3 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -145,13 +145,16 @@ static int cxl_mem_probe(struct device *dev)
> return rc;
>
> rc = devm_cxl_enumerate_ports(cxlmd);
> - if (rc)
> + if (rc) {
> + cxlmd->endpoint = ERR_PTR(rc);
> return rc;
> + }
>
> parent_port = cxl_mem_find_port(cxlmd, &dport);
> if (!parent_port) {
> dev_err(dev, "CXL port topology not found\n");
> - return -ENXIO;
> + cxlmd->endpoint = ERR_PTR(-EPROBE_DEFER);
> + return -EPROBE_DEFER;
> }
>
> if (resource_size(&cxlds->pmem_res) &&
> IS_ENABLED(CONFIG_CXL_PMEM)) { diff --git
> a/drivers/net/ethernet/sfc/efx_cxl.c
> b/drivers/net/ethernet/sfc/efx_cxl.c index 0abe66490ef5..2cf4837ddfc1
> 100644 --- a/drivers/net/ethernet/sfc/efx_cxl.c +++
> b/drivers/net/ethernet/sfc/efx_cxl.c @@ -65,8 +65,16 @@ void
> efx_cxl_init(struct efx_nic *efx) }
>
> cxl->cxlmd = devm_cxl_add_memdev(&pci_dev->dev, cxl->cxlds);
> - if (IS_ERR(cxl->cxlmd))
> + if (IS_ERR(cxl->cxlmd)) {
> pci_info(pci_dev, "CXL accel memdev creation
> failed");
> + return;
> + }
> +
> + cxl->endpoint = cxl_acquire_endpoint(cxl->cxlmd);
> + if (IS_ERR(cxl->endpoint))
> + pci_info(pci_dev, "CXL accel acquire endpoint
> failed"); +
> + cxl_release_endpoint(cxl->cxlmd, cxl->endpoint);
> }
>
>
> diff --git a/include/linux/cxl_accel_mem.h
> b/include/linux/cxl_accel_mem.h index 442ed9862292..701910021df8
> 100644 --- a/include/linux/cxl_accel_mem.h
> +++ b/include/linux/cxl_accel_mem.h
> @@ -29,4 +29,7 @@ int cxl_await_media_ready(struct cxl_dev_state
> *cxlds);
> struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
> struct cxl_dev_state *cxlds);
> +
> +struct cxl_port *cxl_acquire_endpoint(struct cxl_memdev *cxlmd);
> +void cxl_release_endpoint(struct cxl_memdev *cxlmd, struct cxl_port
> *endpoint); #endif
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