linux-kernel - Re: [PATCH v10 3/3] nvmem: core: Expose cells through sysfs

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Message-ID: <20231001175942.749d9bb3@xps-13>
Date:   Sun, 1 Oct 2023 17:59:42 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Rafał Miłecki <rafal@...ecki.pl>
Cc:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michael Walle <michael@...le.cc>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Robert Marko <robert.marko@...tura.hr>,
        Luka Perkov <luka.perkov@...tura.hr>,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Chen-Yu Tsai <wenst@...omium.org>,
        Daniel Golle <daniel@...rotopia.org>
Subject: Re: [PATCH v10 3/3] nvmem: core: Expose cells through sysfs

Hi Rafał,

rafal@...ecki.pl wrote on Fri, 29 Sep 2023 07:18:32 +0200:

> On 2023-09-28 17:31, Rafał Miłecki wrote:
> > On 2023-09-22 19:48, Miquel Raynal wrote:  
> >> The binary content of nvmem devices is available to the user so in the
> >> easiest cases, finding the content of a cell is rather easy as it is
> >> just a matter of looking at a known and fixed offset. However, nvmem
> >> layouts have been recently introduced to cope with more advanced
> >> situations, where the offset and size of the cells is not known in
> >> advance or is dynamic. When using layouts, more advanced parsers are
> >> used by the kernel in order to give direct access to the content of >> each
> >> cell, regardless of its position/size in the underlying
> >> device. Unfortunately, these information are not accessible by users,
> >> unless by fully re-implementing the parser logic in userland.  
> >> >> Let's expose the cells and their content through sysfs to avoid these  
> >> situations. Of course the relevant NVMEM sysfs Kconfig option must be
> >> enabled for this support to be available.  
> >> >> Not all nvmem devices expose cells. Indeed, the .bin_attrs attribute  
> >> group member will be filled at runtime only when relevant and will
> >> remain empty otherwise. In this case, as the cells attribute group >> will
> >> be empty, it will not lead to any additional folder/file creation.  
> >> >> Exposed cells are read-only. There is, in practice, everything in the  
> >> core to support a write path, but as I don't see any need for that, I
> >> prefer to keep the interface simple (and probably safer). The >> interface
> >> is documented as being in the "testing" state which means we can later
> >> add a write attribute if though relevant.  
> >> >> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>  
> > 
> > Tested-by: Rafał Miłecki <rafal@...ecki.pl>
> > 
> > # hexdump -C /sys/bus/nvmem/devices/u-boot-env0/cells/ipaddr@15c
> > 00000000  31 39 32 2e 31 36 38 2e  31 2e 31                 > |192.168.1.1|
> > 0000000b  
> 
> The same test after converting U-Boot env into layout driver:
> 
> # hexdump -C /sys/bus/nvmem/devices/mtd1/cells/ipaddr@15c
> 00000000  31 39 32 2e 31 36 38 2e  31 2e 31                 |192.168.1.1|
> 0000000b
> 
> Looks good!
> 

Great! Thanks a lot for testing!

Miquèl