linux-kernel - Re: [PATCH 2/2] mfd: intel-m10-bmc: add access table configuration to the regmap

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Date:   Thu, 21 Jan 2021 16:05:54 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Tom Rix <trix@...hat.com>
Cc:     lee.jones@...aro.org, linux-kernel@...r.kernel.org,
        matthew.gerlach@...ux.intel.com, russell.h.weight@...el.com,
        lgoncalv@...hat.com, hao.wu@...el.com, yilun.xu@...el.com
Subject: Re: [PATCH 2/2] mfd: intel-m10-bmc: add access table configuration
 to  the regmap

On Wed, Jan 20, 2021 at 07:32:53AM -0800, Tom Rix wrote:
> 
> On 1/19/21 6:34 PM, Xu Yilun wrote:
> > From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> >
> > This patch adds access tables to the MAX 10 BMC regmap. This prevents
> > the host from accessing the unwanted I/O space. It also filters out the
> > invalid outputs when reading the regmap debugfs interface.
> >
> > Signed-off-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> > Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> > ---
> >  drivers/mfd/intel-m10-bmc.c       | 14 ++++++++++++++
> >  include/linux/mfd/intel-m10-bmc.h |  5 ++++-
> >  2 files changed, 18 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mfd/intel-m10-bmc.c b/drivers/mfd/intel-m10-bmc.c
> > index b84579b..0ae3053 100644
> > --- a/drivers/mfd/intel-m10-bmc.c
> > +++ b/drivers/mfd/intel-m10-bmc.c
> > @@ -23,10 +23,24 @@ static struct mfd_cell m10bmc_pacn3000_subdevs[] = {
> >  	{ .name = "n3000bmc-secure" },
> >  };
> >  
> > +static const struct regmap_range m10bmc_regmap_range[] = {
> > +	regmap_reg_range(M10BMC_LEGACY_SYS_BASE + M10BMC_BUILD_VER,
> > +			 M10BMC_LEGACY_SYS_BASE + M10BMC_BUILD_VER),
> 
> If this is the only value in the legacy map to be accessed, could it have its own #define ?
> 
> Something like
> 
> #define M10BMC_LEGACY_BUILD_VER ?

Yes, it could be more clear. I'll change it.

> 
> > +	regmap_reg_range(M10BMC_SYS_BASE, M10BMC_SYS_END),
> > +	regmap_reg_range(M10BMC_FLASH_BASE, M10BMC_FLASH_END),
> > +};
> > +
> > +static const struct regmap_access_table m10bmc_access_table = {
> > +	.yes_ranges	= m10bmc_regmap_range,
> > +	.n_yes_ranges	= ARRAY_SIZE(m10bmc_regmap_range),
> > +};
> > +
> >  static struct regmap_config intel_m10bmc_regmap_config = {
> >  	.reg_bits = 32,
> >  	.val_bits = 32,
> >  	.reg_stride = 4,
> > +	.wr_table = &m10bmc_access_table,
> > +	.rd_table = &m10bmc_access_table,
> 
> The legacy build ver should only be read, so shouldn't these tables be different ?

I'm not sure if a register could be regarded as writable if hardware
ensures writing it has no effect but makes no harm. Usually these
registers are marked as RO in spec.

I think it could be quite common case in hardware design. But it could
be trivial if we pick every such register out of wr_table. I just want
to define the valid reg range.

So could I keep the current implementation?

Thanks,
Yilun