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Piccoli" , Florian Fainelli , Arend van Spriel , William Zhang , bcm-kernel-feedback-list@broadcom.com, linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org, Kamal Dasu Subject: [PATCH v4 1/4] mmc: core: Add panic-context host operations for pstore backends Date: Fri, 20 Mar 2026 16:32:46 -0400 Message-Id: <20260320203249.1965044-2-kamal.dasu@broadcom.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260320203249.1965044-1-kamal.dasu@broadcom.com> References: <20260320203249.1965044-1-kamal.dasu@broadcom.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-DetectorID-Processed: b00c1d49-9d2e-4205-b15f-d015386d3d5e Content-Type: text/plain; charset="utf-8" Add three new optional callbacks to struct mmc_host_ops for panic-safe MMC I/O: - panic_prepare: drain in-flight requests and prepare for polled I/O - panic_poll_completion: poll for request completion without interrupts - panic_complete: restore normal host state after panic I/O Add mmc_panic_claim_host() which uses WRITE_ONCE() to claim the host without taking the spin lock, since during panic other CPUs are stopped and may hold the lock. Signed-off-by: Kamal Dasu --- drivers/mmc/core/core.c | 23 +++++++++++++++++++++++ include/linux/mmc/host.h | 12 ++++++++++++ 2 files changed, 35 insertions(+) diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c index 860378bea557..5326b246b4f2 100644 --- a/drivers/mmc/core/core.c +++ b/drivers/mmc/core/core.c @@ -860,6 +860,29 @@ void mmc_release_host(struct mmc_host *host) } EXPORT_SYMBOL(mmc_release_host); =20 +/** + * mmc_panic_claim_host - force-claim a host in panic context + * @host: mmc host to claim + * + * Force-claims the MMC host without locking. During kernel panic + * other CPUs are stopped and may be holding mmc_host->lock (e.g. + * inside __mmc_claim_host or mmc_release_host). Unlike sdhci_host->lock + * which is freed by the hardware drain+reset, mmc_host->lock has no + * hardware counterpart, so we must bypass it with WRITE_ONCE. + */ +void mmc_panic_claim_host(struct mmc_host *host) +{ + if (!host) + return; + + WRITE_ONCE(host->claimed, 1); + host->claimer =3D &host->default_ctx; + host->claimer->task =3D current; + WRITE_ONCE(host->claim_cnt, 1); + WRITE_ONCE(host->ongoing_mrq, NULL); +} +EXPORT_SYMBOL(mmc_panic_claim_host); + /* * This is a helper function, which fetches a runtime pm reference for the * card device and also claims the host. diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h index ba84f02c2a10..cd44b62d29cb 100644 --- a/include/linux/mmc/host.h +++ b/include/linux/mmc/host.h @@ -272,6 +272,16 @@ struct mmc_host_ops { * negative errno in case of a failure or zero for success. */ int (*uhs2_control)(struct mmc_host *host, enum sd_uhs2_operation op); + + /* + * Optional panic-context ops for pstore backends that write to MMC + * during kernel panic with interrupts disabled. + */ + int (*panic_prepare)(struct mmc_host *host); + bool (*panic_poll_completion)(struct mmc_host *host, + struct mmc_request *mrq); + void (*panic_complete)(struct mmc_host *host, + struct mmc_request *mrq); }; =20 struct mmc_cqe_ops { @@ -758,4 +768,6 @@ int mmc_send_abort_tuning(struct mmc_host *host, u32 op= code); int mmc_get_ext_csd(struct mmc_card *card, u8 **new_ext_csd); int mmc_read_tuning(struct mmc_host *host, unsigned int blksz, unsigned in= t blocks); =20 +void mmc_panic_claim_host(struct mmc_host *host); + #endif /* LINUX_MMC_HOST_H */ --=20 2.34.1