Re: [PATCH 2/7] firmware: add offset to request_firmware_into_buf

From: Scott Branden <scott.branden@broadcom.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
	Takashi Iwai <tiwai@suse.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	David Brown <david.brown@linaro.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Shuah Khan <shuah@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	Shuah Khan <skhan@linuxfoundation.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
	Olof Johansson <olof@lixom.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Colin Ian King <colin.king@canonical.com>,
	Kees Cook <keescook@chromium.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH 2/7] firmware: add offset to request_firmware_into_buf
Date: Fri, 21 Feb 2020 10:23:21 -0800	[thread overview]
Message-ID: <c3bf2985-78d3-ae98-a19d-a596f42a22ce@broadcom.com> (raw)
In-Reply-To: <CAK8P3a2NJurg_hxVbWYZwJVhYM5-xjWt12Kh0DdyfTGqQPrPAQ@mail.gmail.com>


On 2020-02-21 12:44 a.m., Arnd Bergmann wrote:
> On Fri, Feb 21, 2020 at 1:11 AM Scott Branden
> <scott.branden@broadcom.com> wrote:
>> On 2019-10-11 6:31 a.m., Luis Chamberlain wrote:
>>> On Tue, Aug 27, 2019 at 12:40:02PM +0200, Takashi Iwai wrote:
>>>> On Mon, 26 Aug 2019 19:24:22 +0200,
>>>> Scott Branden wrote:
>>>>> I will admit I am not familiar with every subtlety of PCI
>>>>> accesses. Any comments to the Valkyrie driver in this patch series are
>>>>> appreciated.
>>>>> But not all drivers need to work on all architectures. I can add a
>>>>> depends on x86 64bit architectures to the driver to limit it to such.
>>>> But it's an individual board on PCIe, and should work no matter which
>>>> architecture is?  Or is this really exclusive to x86?
>>> Poke Scott.
>> Yes, this is exclusive to x86.
>> In particular, 64-bit x86 server class machines with PCIe gen3 support.
>> There is no reason for these PCIe boards to run in other lower end
>> machines or architectures.
> It doesn't really matter that much what you expect your customers to
> do with your product, or what works a particular machine today, drivers
> should generally be written in a portable manner anyway and use
> the documented APIs. memcpy() into an __iomem pointer is not
> portable and while it probably works on any x86 machine today, please
> just don't do it. If you use 'sparse' to check your code, that would normally
> result in an address space warning, unless you add __force and a
> long comment explaining why you cannot just use memcpy_to_io()
> instead. At that point, you are already better off usingn memcpy_to_io() ;-)
We don't want to allocate to intermediate memory and do another memcpy 
just to write to pcie.
I will have to look into the linux request_firmware_info_buf code and 
detect whether the buf being request to is
in kernel or io memory and perform the operation there.  Hopefully such 
is possible.
>
>          Arnd