linux-kernel - [RFC PATCH 0/1] Verify if register is writeable before a write operation

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Date:   Tue, 2 Apr 2019 08:01:21 +0000
From:   Han Nandor <nandor.han@...sala.com>
To:     "broonie@...nel.org" <broonie@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Han Nandor <nandor.han@...sala.com>
Subject: [RFC PATCH 0/1] Verify if register is writeable before a write
 operation

Description
-----------
This is an RFC because I don't know if this is a bug or a normal use
case. It seems that the function `_regmap_raw_write_impl` from the regmap
framework verifies that a register is writable only using
the callback function, ignoring the other two (max allowed register,
register ranges)

Note: As a left right look I did check also `_regmap_raw_read` function,
and it seems that is missing this checks completely.
Is this a problem as well?

Device/Subsystems Impacted
-------------------------
This will impact drivers that end up using raw writes (firmware
download, ...)


Testing
-------
Test configuration:
- Kernel Version: 4.14.60 (just for clarification, the patch is rebased on master)
- The testing was done using a driver that has NVMEM support and is
  using `regmap_bulk_write` method to write data to registers.
- The valid register range is 0x00->0xFF.

1. Configure a nvcell (4 bytes long) in DT which is outside the valid register range.
2. Write data to NVMEM using the nvcell
3. Verify the result:
3.1 Without the patch the data write in registers is successful with
no error displayed.
3.2 With the patch the data write is denied and an error is displayed.

Nandor Han (1):
  regmap: verify if register is writeable before writing operations

 drivers/base/regmap/regmap.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

-- 
2.17.2