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

From: Mark Brown <broonie@kernel.org>
To: Paul Cercueil <paul.cercueil@bootlin.com>
Cc: Pratyush Yadav <pratyush@kernel.org>,
	Michael Walle <mwalle@kernel.org>,
	Takahiro Kuwano <takahiro.kuwano@infineon.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	Kees Cook <kees@kernel.org>, Tony Luck <tony.luck@intel.com>,
	"Guilherme G . Piccoli" <gpiccoli@igalia.com>,
	linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-spi@vger.kernel.org, Tanmay Jagdale <tanmay@marvell.com>
Subject: Re: [PATCH 1/5] spi: spi-mem: Add support for panic mem writes
Date: Thu, 8 Oct 2026 10:32:51 +0200	[thread overview]
Message-ID: <asdVM883VTQy7WvH@sirena.co.uk> (raw)
In-Reply-To: <20261005081141.33688-2-paul.cercueil@bootlin.com>

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On Mon, Oct 05, 2026 at 10:11:36AM +0200, Paul Cercueil wrote:
> From: Tanmay Jagdale <tanmay@marvell.com>
> 
> 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.

> --- 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.
> +		 */

This also needs to ensure that the queue is idle - we'll still execute
spi_mem_access_start() which flushes the queue, and we've got runtime PM
operations there which might be a bit challenging in a panic situation.

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