Re: [PATCH] regmap: spi: Reserve space for register address/padding

[Cristian Ciocaltea]

On 8/18/22 12:22, Lucas tanure wrote:
> On 8/17/22 22:38, Cristian Ciocaltea wrote:
> > Currently the max_raw_read and max_raw_write limits in regmap_spi struct
> > do not take into account the additional size of the transmitted register
> > address and padding.  This may result in exceeding the maximum permitted
> > SPI transfer size, which could cause undefined behaviour, e.g. data
> > corruption.
> >
> > Fix regmap_get_spi_bus() to properly adjust the above mentioned limits
> > by reserving space for the register address/padding as set in the regmap
> > configuration.
> >
> > Fixes: f231ff38b7b2 ("regmap: spi: Set regmap max raw r/w from 
> > max_transfer_size")
> >
> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> > ---
> >   drivers/base/regmap/regmap-spi.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/base/regmap/regmap-spi.c 
> > b/drivers/base/regmap/regmap-spi.c
> > index 719323bc6c7f..6fb94c06a447 100644
> > --- a/drivers/base/regmap/regmap-spi.c
> > +++ b/drivers/base/regmap/regmap-spi.c
> > @@ -113,6 +113,7 @@ static const struct regmap_bus 
> > *regmap_get_spi_bus(struct spi_device *spi,
> >                              const struct regmap_config *config)
> >   {
> >       size_t max_size = spi_max_transfer_size(spi);
> > +    size_t max_msg_size, reg_reserve_size;
> >       struct regmap_bus *bus;
> >
> >       if (max_size != SIZE_MAX) {
> > @@ -120,9 +121,15 @@ static const struct regmap_bus 
> > *regmap_get_spi_bus(struct spi_device *spi,
> >           if (!bus)
> >               return ERR_PTR(-ENOMEM);
> >
> > +        max_msg_size = spi_max_message_size(spi);
> > +        reg_reserve_size = config->reg_bits / 8 + config->pad_bits / 8;
> I think you can use BITS_PER_BYTE here instead of 8.

Right, thanks for hint. Applied to v2:

https://lore.kernel.org/all/20220818104851.429479-1-cristian.ciocaltea@xxxxxxxxxxxxx/

> > +        if (max_size + reg_reserve_size > max_msg_size)
> > +            max_size -= reg_reserve_size;
> > +
> >           bus->free_on_exit = true;
> >           bus->max_raw_read = max_size;
> >           bus->max_raw_write = max_size;
> > +
> >           return bus;
> >       }
> >
> > base-commit: 568035b01cfb107af8d2e4bd2fb9aea22cf5b868
> > --
> > 2.37.2