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

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Paul Cercueil <paul.cercueil@bootlin.com>
Cc: Mark Brown <broonie@kernel.org>,
	 Pratyush Yadav <pratyush@kernel.org>,
	Michael Walle <mwalle@kernel.org>,
	 Takahiro Kuwano <takahiro.kuwano@infineon.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: Tue, 13 Oct 2026 10:38:26 +0200	[thread overview]
Message-ID: <87y0c2vvul.fsf@bootlin.com> (raw)
In-Reply-To: <5c94b88bf7123e5a32d5c4bd77217e6a40683c83.camel@bootlin.com> (Paul Cercueil's message of "Tue, 13 Oct 2026 10:25:07 +0200")

On 13/10/2026 at 10:25:07 +02, Paul Cercueil <paul.cercueil@bootlin.com> wrote:

> Hi Mark,
>
> Le jeudi 08 octobre 2026 à 10:32 +0200, Mark Brown a écrit :
>> 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.
>
> Does it though? The kernel is panicking so the queue won't be processed anymore,
> it should be fine to just ignore it.
>
> ACK for the PM - I think in the V2 I'll just bail if the controller has auto-
> runtime-PM on.

Maybe pm_runtime_get_if_active()? If already active it returns 1 and
you can proceed.

Thanks,
Miquèl