Re: [PATCH v4] mtd: parsers: ofpart: add workaround for #size-cells 0

[Miquel Raynal <miquel.raynal@bootlin.com>]

Hi Greg,

francesco@dolcini.it wrote on Wed, 25 Jan 2023 22:06:57 +0100:

> Hello Miquel, Greg and all
> 
> On Tue, Jan 24, 2023 at 04:38:59PM +0100, Greg Kroah-Hartman wrote:
> > On Tue, Jan 24, 2023 at 11:44:44AM +0100, Francesco Dolcini wrote:  
> > > From: Francesco Dolcini <francesco.dolcini@toradex.com>
> > > 
> > > Add a mechanism to handle the case in which partitions are present as
> > > direct child of the nand controller node and #size-cells is set to <0>.
> > > 
> > > This could happen if the nand-controller node in the DTS is supposed to
> > > have #size-cells set to 0, but for some historical reason/bug it was set
> > > to 1 in the past, and the firmware (e.g. U-Boot) is adding the partition
> > > as direct children of the nand-controller defaulting to #size-cells
> > > being to 1.
> > > 
> > > This prevents a real boot failure on colibri-imx7 that happened during v6.1
> > > development cycles.
> > > 
> > > Link: https://lore.kernel.org/all/Y4dgBTGNWpM6SQXI@francesco-nb.int.toradex.com/
> > > Link: https://lore.kernel.org/all/20221202071900.1143950-1-francesco@dolcini.it/
> > > Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
> > > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > ---
> > > I do not expect this patch to be backported to stable, however I would expect
> > > that we do not backport nand-controller dts cleanups neither.
> > > 
> > > v4:
> > >  fixed wrong English spelling in the comment
> > > 
> > > v3:
> > >  minor formatting change, removed not needed new-line and space. 
> > > 
> > > v2:
> > >  fixup size-cells only when partitions are direct children of the nand-controller
> > >  completely revised commit message, comments and warning print
> > >  use pr_warn instead of pr_warn_once
> > >  added Reviewed-by Greg
> > >  removed cc:stable@ and fixes tag, since the problematic commit was reverted
> > > ---
> > >  drivers/mtd/parsers/ofpart_core.c | 19 +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > > 
> > > diff --git a/drivers/mtd/parsers/ofpart_core.c b/drivers/mtd/parsers/ofpart_core.c
> > > index 192190c42fc8..e7b8e9d0a910 100644
> > > --- a/drivers/mtd/parsers/ofpart_core.c
> > > +++ b/drivers/mtd/parsers/ofpart_core.c
> > > @@ -122,6 +122,25 @@ static int parse_fixed_partitions(struct mtd_info *master,
> > >  
> > >  		a_cells = of_n_addr_cells(pp);
> > >  		s_cells = of_n_size_cells(pp);
> > > +		if (!dedicated && s_cells == 0) {
> > > +			/*
> > > +			 * This is a ugly workaround to not create
> > > +			 * regression on devices that are still creating
> > > +			 * partitions as direct children of the nand controller.
> > > +			 * This can happen in case the nand controller node has
> > > +			 * #size-cells equal to 0 and the firmware (e.g.
> > > +			 * U-Boot) just add the partitions there assuming
> > > +			 * 32-bit addressing.
> > > +			 *
> > > +			 * If you get this warning your firmware and/or DTS
> > > +			 * should be really fixed.
> > > +			 *
> > > +			 * This is working only for devices smaller than 4GiB.
> > > +			 */
> > > +			pr_warn("%s: ofpart partition %pOF (%pOF) #size-cells is wrongly set to <0>, assuming <1> for parsing partitions.\n",
> > > +				master->name, pp, mtd_node);  
> > 
> > This is a driver, always use dev_*() calls, not pr_*() calls so that we
> > know what is being referred to exactly.  
> 
> Is this reasonable here? Where can I get the struct device?
> 
> In general this file uses only pr_* debug API and messages are about OF
> nodes/properties, not about a device.

I'm also skeptical here, this is not a device driver, it's a generic
parser and it seems more appropriate to warn about an of node rather
than a struct device.

MTD devices inherit from struct device (mtd->dev) which I guess
might be used here. The bus infrastructure device
(mtd->device->parents) is less appropriate as it sometimes points at the
controller (raw NAND) and sometimes at the spi device (SPI-NAND, SPI
NOR).

pr_warn is fine here IMHO, but if Greg insist, switch it to dev_warn, I
don't mind. Maybe it is worth testing that dev_warn still displays an
easy-to-understand message in that case.

> > I take back my "reviewed-by" line above, please fix this up to not need
> > pr_warn, but to use dev_warn() instead.  
> 
> Francesco


Thanks,
Miquèl

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