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 05:19:56 -0800
From:   Tom Rix <trix@...hat.com>
To:     Xu Yilun <yilun.xu@...el.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
Subject: Re: [PATCH 2/2] mfd: intel-m10-bmc: add access table configuration to
 the regmap


On 1/21/21 12:05 AM, Xu Yilun wrote:
> 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?

I mean that the write table would not have first element the read table has because it has the single ro entry.

The other ranges i am sure have ro's and are not worth breaking apart.

If something like

.wr_table = &m10bmc_access_table[1] doesn't work or looks to hacky, i don't mind leaving it as-is.

Tom

>
> Thanks,
> Yilun
>