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

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

Hi Francesco,

francesco@dolcini.it wrote on Thu, 2 Feb 2023 12:33:34 +0100:

> On Thu, Jan 26, 2023 at 10:12:04AM +0100, Miquel Raynal wrote:
> > gregkh@linuxfoundation.org wrote on Thu, 26 Jan 2023 10:01:02 +0100:
> >   
> > > On Wed, Jan 25, 2023 at 10:06:57PM +0100, Francesco Dolcini wrote:  
> > > > 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?    
> > > 
> > > Walk back up the call chain, there has to be a device somewhere
> > > controlling this, right?
> > >   
> > > > In general this file uses only pr_* debug API and messages are about OF
> > > > nodes/properties, not about a device.    
> > > 
> > > OF nodes and properties are part of a device's properties :)  
> > 
> > Yes but the warning comes from a wrong DT description, hence it felt
> > better suited to warn against the node name which is easily identifiable
> > in a text file and must be fixed rather than the device which is a pure
> > software component.
> > 
> > Anyway, Francesco, please show us the resultant line and if it feels
> > meaningful enough we'll take the dev_warn approach.  
> 
> So, I tried, but I guess I failed.
> 
> Both
> 
>   dev_warn(&mtd_get_master(master)->dev, ...);
> 
> and
> 
>   dev_warn(&master->dev, ...);
> 
> are NULL.

mtd->dev (in raw NAND) is populated by the controller drivers, so the
master mtd device is pointing to the bus "struct device" in its
dev.parent field. This happens at the end of the probe of the
controller, after setting the dev entry, so we expect the name of the
controller to appear.

> (null): gpmi-nand: ofpart partition /soc/nand-controller@33002000/partition@0 (/soc/nand-controller@33002000) #size-cells is wrongly set to <0>, assuming <1> for parsing partitions.

Second field looks right, first field does not (bus or class id?) I
have no idea why it has not been populated at this point (end of the
controller probe). But it's not a big deal, at least we have the device
name, so it's ok for me.

> while the current v4 is just:
> 
> gpmi-nand: ofpart partition /soc/nand-controller@33002000/partition@0 (/soc/nand-controller@33002000) #size-cells is wrongly set to <0>, assuming <1> for parsing partitions.
> 
> on a colibri-imx7.
> 
> Any advice?
> 
> Francesco
> 


Thanks,
Miquèl