From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v15 06/16] of/fdt: add helper functions for handling properties References: <20180928064841.14117-1-takahiro.akashi@linaro.org> <20180928064841.14117-7-takahiro.akashi@linaro.org> <20181005030849.GK32578@linaro.org> <20181009003733.GN32578@linaro.org> From: Frank Rowand Message-ID: Date: Tue, 9 Oct 2018 10:47:15 -0700 MIME-Version: 1.0 In-Reply-To: <20181009003733.GN32578@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit To: "AKASHI, Takahiro" , Rob Herring , David Gibson , Catalin Marinas , Will Deacon , David Howells , Vivek Goyal , Herbert Xu , David Miller , dyoung@redhat.com, Baoquan He , Arnd Bergmann , Martin Schwidefsky , Heiko Carstens , prudo@linux.ibm.com, Ard Biesheuvel , James Morse , bhsharma@redhat.com, kexec@lists.infradead.org, "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" , "linux-kernel@vger.kernel.org" , devicetree@vger.kernel.org, Frank Rowand List-ID: On 10/08/18 17:37, AKASHI, Takahiro wrote: > On Fri, Oct 05, 2018 at 08:23:57AM -0500, Rob Herring wrote: >> On Thu, Oct 4, 2018 at 10:07 PM AKASHI, Takahiro >> wrote: >>> >>> Rob, >>> >>> # I haven't replied to this comment yet. >>> >>> On Fri, Sep 28, 2018 at 08:44:42AM -0500, Rob Herring wrote: >>>> +David Gibson >>>> >>>> On Fri, Sep 28, 2018 at 1:48 AM AKASHI Takahiro >>>> wrote: >>>>> >>>>> These functions will be used later to handle kexec-specific properties >>>>> in arm64's kexec_file implementation. >>>>> >>>>> Signed-off-by: AKASHI Takahiro >>>>> Cc: Rob Herring >>>>> Cc: Frank Rowand >>>>> Cc: devicetree@vger.kernel.org >>>>> --- >>>>> drivers/of/fdt.c | 56 ++++++++++++++++++++++++++++++++++++++++++ >>>>> include/linux/of_fdt.h | 4 +++ >>>>> 2 files changed, 60 insertions(+) >>>>> >>>>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >>>>> index 800ad252cf9c..c65c31562ccb 100644 >>>>> --- a/drivers/of/fdt.c >>>>> +++ b/drivers/of/fdt.c >>>>> @@ -25,6 +25,7 @@ >>>>> #include >>>>> #include >>>>> #include >>>>> +#include >>>>> >>>>> #include /* for COMMAND_LINE_SIZE */ >>>>> #include >>>>> @@ -1323,3 +1324,58 @@ late_initcall(of_fdt_raw_init); >>>>> #endif >>>>> >>>>> #endif /* CONFIG_OF_EARLY_FLATTREE */ >>>>> + >>>>> +#define FDT_ALIGN(x, a) (((x) + (a) - 1) & ~((a) - 1)) >>>>> +#define FDT_TAGALIGN(x) (FDT_ALIGN((x), FDT_TAGSIZE)) >>>>> + >>>>> +int fdt_prop_len(const char *prop_name, int len) >>>>> +{ >>>>> + return (strlen(prop_name) + 1) + >>>>> + sizeof(struct fdt_property) + >>>>> + FDT_TAGALIGN(len); >>>> >>>> Looks like you are using this to calculate how much space you need to >>>> allocate in addition to the current DTB for a couple of new or >>>> replaced properties. I'm not sure that this calculation is completely >>>> accurate. And it is strange there doesn't seem to be any libfdt >>>> function for this already. It would be simpler to just add some fixed >>>> additional amount. >>>> >>>> Maybe David G has comments on this? >>>> >>>>> +} >>>>> + >>>> >>>> The rest of this should go in drivers/of/fdt_address.c. Ultimately, it >>>> should go into libfdt, but I'm fine with having it in the kernel for >>>> now. >>> >>> I'd like to have this function in the kernel for now. >>> >>>>> +static void fill_property(void *buf, u64 val64, int cells) >>>>> +{ >>>>> + __be32 val32; >>>>> + >>>>> + while (cells) { >>>>> + val32 = cpu_to_fdt32((val64 >> (32 * (--cells))) & U32_MAX); >>>>> + memcpy(buf, &val32, sizeof(val32)); >>>>> + buf += sizeof(val32); >>>> >>>> This is kind of hard to read. I would copy u-boot's fdt_pack_reg function. >>> >>> Are you sure? >>> I originally implemented this function in a similar way that fdt_pack_reg() >>> was, but, you suggested, in your past comment[1], that we'd be better to >>> have of_read_number()-like implementation. >>> >>> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-May/579118.html >> >> Yeah, you're right. Plus, I'm not sure the u-boot one would work for >> unaligned accesses with armv5 and earlier h/w. >> >> My only comment then is I think you can drop the U32_MAX masking. > > Okay, then I will leave this function, yet renaming it to > cpu64_to_fdt_cells() after Frank's comment. I have second guessed myself and do not like the name I suggested because what the function really does is either cpu32 to be32 or cpu64 to be64. I agree with Rob that readability is important here. Instead of having a fill_property() function, how about having inline code, something like (untested even for thinkos): prop = buf; if (addr_cells == 1) { *(__be32 *)prop = cpu32_to_be32(addr); prop += 4; } else { *(__be64 *)prop = cpu64_to_be64(addr); prop += 8; } if (size_cells == 1) *(__be32 *)prop = cpu32_to_be32(size); else *(__be64 *)prop = cpu64_to_be64(size); You might want to also give Rob a chance to bike shed on this suggestion. -Frank > > Thanks, > -Takahiro Akashi >> >> Rob >