Re: [PATCH 5/5] net/cxgbe: read firmware configuration file from filesystem

[Thomas Monjalon <thomas@monjalon.net>]

10/05/2022 17:05, Rahul Lakkireddy:
> On Tuesday, May 05/10/22, 2022 at 16:30:59 +0200, Thomas Monjalon wrote:
> > 10/05/2022 16:11, Rahul Lakkireddy:
> > > On Tuesday, May 05/10/22, 2022 at 11:02:05 +0200, Thomas Monjalon wrote:
> > > > 06/05/2022 13:36, Rahul Lakkireddy:
> > > > > The Chelsio FW config file contains a list of register=value pairs to
> > > > > change configuration of the NIC before firmware is initialized.
> > > > > It closely resembles the INI file format. It is mainly used to aid
> > > > > in debugging FW initialization failures and to optimally partition
> > > > > NIC hardware resources for specific requirements. Partitioning
> > > > > generally involves moving resources on unused Physical Functions
> > > > > (PFs) to the main PF, like redistributing queues, hardware TCAMs,
> > > > > etc., before firmware begins initialization. Once the configuration
> > > > > looks good, then the final FW config file is flashed onto the NIC
> > > > > using the cxgbtool. The FW config file can then be removed from the
> > > > > /lib/firmware/cxgb4/ directory and the FW will begin initializing
> > > > > with the flashed FW config file on the NIC from next time onwards.
> > > > > 
> > > > > With this patch, the FW config file is selected in following order.
> > > > > 
> > > > > 1) Check and select FW config file present in /lib/firmware/cxgb4/
> > > > >    directory.
> > > > > 
> > > > > 2) Otherwise, check and select FW config file flashed onto the
> > > > >    NIC.
> > > > > 
> > > > > 3) Otherwise, select the default FW config file embedded within the
> > > > >    FW binary on the NIC.
> > > > > 
> > > > > Since this is pretty low-level hardware configuration, the users are
> > > > > not expected to change this file without expert guidance. So,
> > > > > exporting such a low-level configuration via devargs API does not
> > > > > feel like the right fit for this specific requirement.
> > > > > 
> > > > > Once FW is up and running with the FW config file, some of the driver
> > > > > and FW runtime features can be enabled/disabled via devargs API during
> > > > > driver probe.
> > > > > 
> > > > > To summarize, the FW config file is intended to debug FW initialization
> > > > > failures and/or aid in resources partitioning before FW starts
> > > > > initialization. Once the FW is running, the whole or smaller slices
> > > > > of these partitioned resources can be further redistributed across
> > > > > the multiple physical ports controlled by the same underlying PF.
> > > > 
> > > > Sorry it is not clear to me.
> > > > The FW file is used by cxgbtool to flash it, right?
> > > > The PMD may use the same FW file for debug diagnostics?
> > > 
> > > 
> > > There are 2 FW related files in /lib/firmware/cxgb4 directory that
> > > can be written into the NIC flash (at different locations in the flash)
> > > using cxgbtool:
> > > 
> > > 1) FW config file (t6-config.txt): This file contains register=value
> > >    pairs to configure some HW registers before initializing FW
> > >    (t6fw.bin). These register=value pairs are very low level and
> > >    specific to HW. The FW config file can be used to enable/disable
> > >    some paths in HW to debug FW initialization issues. Since it
> > >    can disable some paths in HW, it can also be used to partition
> > >    and redistribute resources from other unused PFs to main PF,
> > >    before FW initialization.
> > > 
> > > 2) FW binary (t6fw.bin): This contains the actual FW. This binary also
> > >    has an embedded "default" FW config file that will be used if no
> > >    FW config file (t6-config.txt) is present in NIC "flash" or in the
> > >    "/lib/firmware/cxgb4/" directory.
> > > 
> > > > How is it used by the kernel?
> > > > 
> > > 
> > > In kernel cxgb4 driver also, we follow the same sequence when
> > > initializing FW. If any FW config file (t6-config.txt) is present
> > > in "/lib/firmware/cxgb4" directory, then it is picked up first.
> > > Otherwise, a FW config file that has been "flashed" onto the NIC
> > > using cxgbtool, is picked up next. Otherwise, FW will init with
> > > the "default" FW config file embedded inside the FW binary (t6fw.bin).
> > > 
> > > Currently, the DPDK cxgbe PMD only picks up the FW config file from
> > > NIC "flash" or the "default" one inside the FW binary. This patch adds
> > > a way to pick FW config file from "lib/firmware/cxgb4" directory when
> > > a FW config file is placed there.
> > 
> > OK, so both Linux and DPDK drivers read the FW config file
> > to provide better diagnostics. Am I right?
> > 
> 
> Yes, both use the FW config file to enable/disable specific paths in
> HW to get better diagnostics for FW init failures.

OK thanks for the explanation.
The idea looks OK.