[PATCH 1/5] spi: spi-mem: Add support for panic mem writes

[Paul Cercueil]

From: Tanmay Jagdale <tanmay@xxxxxxxxxxx>

Add a 'panic_write' flag to the controller's capabilities struct.
When set, the SPI controller indicates that it will be able to send
commands to a connected NOR or NAND memory in the context of a kernel
panic, which means without sleeping and without relying on IRQs.

Whether or not a given memory operation is a panic mem write is given by
the spi_mem_op.panic_write flag.

Signed-off-by: Tanmay Jagdale <tanmay@xxxxxxxxxxx>
Co-developed-by: Paul Cercueil <paul.cercueil@xxxxxxxxxxx>
Signed-off-by: Paul Cercueil <paul.cercueil@xxxxxxxxxxx>
---
 drivers/spi/spi-mem.c       | 25 +++++++++++++++++++++++++
 include/linux/spi/spi-mem.h |  5 +++++
 2 files changed, 30 insertions(+)

diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
index b94680b60af9..89710f9f555e 100644
--- a/drivers/spi/spi-mem.c
+++ b/drivers/spi/spi-mem.c
@@ -398,6 +398,31 @@ int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
 	u8 *tmpbuf;
 	int ret;
 
+	if (op->panic_write) {
+		if (!spi_mem_controller_is_capable(ctlr, panic_write))
+			return -EOPNOTSUPP;
+
+		/*
+		 * Only support panic writes if we'll go through .exec_op().
+		 * The regular SPI path (spi_sync(), etc.) explicitly mentions
+		 * that it can only be used from a context that may sleep, which
+		 * is not the case on a kernel panic.
+		 * If this changes in the future, this could be reworked, but
+		 * for now this will have to do.
+		 */
+		if (WARN_ON_ONCE(!ctlr->mem_ops || !ctlr->mem_ops->exec_op))
+			return -EOPNOTSUPP;
+
+		if (spi_get_csgpiod(mem->spi, 0))
+			return -EPERM;
+
+		/* On panic IRQs are disabled so we cannot wait on locks */
+		if (mutex_is_locked(&ctlr->bus_lock_mutex) ||
+		    mutex_is_locked(&ctlr->io_mutex)) {
+			return -EPERM;
+		}
+	}
+
 	/* Make sure the operation frequency is correct before going futher */
 	spi_mem_adjust_op_freq(mem, (struct spi_mem_op *)op);
 
diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h
index 0cce6b57242a..2633307bfad5 100644
--- a/include/linux/spi/spi-mem.h
+++ b/include/linux/spi/spi-mem.h
@@ -169,6 +169,7 @@ enum spi_mem_data_dir {
  *		 operation does not involve transferring data
  * @data.buf.in: input buffer (must be DMA-able)
  * @data.buf.out: output buffer (must be DMA-able)
+ * @panic_write: The command is executed in the context of a kernel panic
  * @max_freq: frequency limitation wrt this operation. 0 means there is no
  *	      specific constraint and the highest achievable frequency can be
  *	      attempted.
@@ -211,6 +212,7 @@ struct spi_mem_op {
 		} buf;
 	} data;
 
+	bool panic_write;
 	unsigned int max_freq;
 };
 
@@ -392,6 +394,8 @@ struct spi_controller_mem_ops {
  *                   is a pause in the transfer (eg. internal bus contention or
  *                   DMA arbitration on an interconnect). Features such as NAND
  *                   continuous reads shall not be leveraged.
+ * @panic_write: Set to true if the controller driver supports writing to a
+ *               connected NAND/NOR memory in a kernel panic context
  */
 struct spi_controller_mem_caps {
 	bool dtr;
@@ -400,6 +404,7 @@ struct spi_controller_mem_caps {
 	bool per_op_freq;
 	bool secondary_op_tmpl;
 	bool no_cs_assertion;
+	bool panic_write;
 };
 
 #define spi_mem_controller_is_capable(ctlr, cap)	\
-- 
2.47.3