From: Asherah Connor <ashe@kivikakk.ee>
To: u-boot@lists.denx.de
Subject: [PATCH v3 1/4] arm: x86: qemu: move qfw to DM, include Arm support
Date: Wed, 24 Feb 2021 00:22:54 +0000 [thread overview]
Message-ID: <20210224002254.xckn6g4tcue6cqkd@talia.n4wrvuuuhszuhem3na2pm5saea.px.internal.cloudapp.net> (raw)
In-Reply-To: <d26821d4-dc30-2e17-a2dc-67dbaab6beee@gmx.de>
On 21/02/23 01:02:p, Heinrich Schuchardt wrote:
> On 23.02.21 12:43, Asherah Connor wrote:
> For which architectures does the fw_cfg device exist?
>
> It it is only ARM and X86, than I am missing such a dependency on
> CONFIG_CMD_QFW.
Right now we have:
arch/arm/Kconfig:
...
config ARCH_QEMU
...
imply CMD_QFW
I think we also want this:
arch/x86/cpu/qemu/Kconfig
config QEMU
...
imply CMD_QFW
This is my first time using Kconfig and I'll admit I'm not too certain
where things go.
> If these numbers are constants, why should they be copied to platform
> data? This only increases code size.
>
> I think there is nothing wrong with using constants here.
Okay, excellent. I'll fold those into drivers/misc/qfw_pio.c and get
rid of the qfw_pio_plat struct entirely.
> ARM yield is meant to be used on multi-threaded systems to indicate that
> the thread can be swapped. Why would we need it in U-Boot which is
> single-threaded?
>
> Can't we simply use
>
> while (be32_to_cpu(dma.control) & ~FW_CFG_DMA_ERROR);
>
> with no command in the loop for all architectures?
Good question. This code originated here, where the original (x86-only)
driver used pause:
https://gitlab.denx.de/u-boot/u-boot/-/commit/f60df20aa966c3de850afafe3cce70a51d0b261c#41c93c056084377352da52f1d88fc49288a4846f_0_59
When porting to Arm I used the equivalent.
While U-Boot is single-threaded, the architecture that executes this
instruction is always QEMU, and -- at a guess -- it might be that
pause/yield here lets QEMU finish its part of the DMA faster.
I've run the QEMU tests on arm(64)/x86(_64) without the yield or pause
and they still pass. It might be simply unnecessary, so I'll remove for
now in favour of simplicity and less arch-specific code.
Best,
Asherah
next prev parent reply other threads:[~2021-02-24 0:22 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-23 11:43 [PATCH v3 0/4] Move qfw to DM, add Arm support Asherah Connor
2021-02-23 11:43 ` [PATCH v3 1/4] arm: x86: qemu: move qfw to DM, include " Asherah Connor
2021-02-23 12:59 ` Heinrich Schuchardt
2021-02-23 14:53 ` Tom Rini
2021-02-23 15:54 ` Heinrich Schuchardt
2021-02-23 16:03 ` Tom Rini
2021-02-23 16:15 ` Heinrich Schuchardt
2021-02-23 16:33 ` Tom Rini
2021-02-23 23:54 ` Asherah Connor
2021-02-23 23:58 ` Tom Rini
2021-02-24 0:12 ` Asherah Connor
2021-02-24 0:22 ` Asherah Connor [this message]
2021-02-23 11:43 ` [PATCH v3 2/4] arm: x86: qemu: add UCLASS_QFW, split driver into _pio and _mmio Asherah Connor
2021-02-23 15:58 ` Simon Glass
2021-02-23 11:43 ` [PATCH v3 3/4] arm: x86: qemu: unify qfw driver functions as qfw_ Asherah Connor
2021-02-23 11:43 ` [PATCH v3 4/4] qemu: add sandbox driver and tests Asherah Connor
2021-02-23 12:26 ` Asherah Connor
2021-02-23 15:58 ` Simon Glass
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