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[67.187.90.124]) by smtp.gmail.com with ESMTPSA id r17sm13537371qta.78.2021.01.26.10.26.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Jan 2021 10:26:15 -0800 (PST) Subject: Re: [PATCH] cmd_dtc: Enable generation of device tree symbols To: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Masahiro Yamada , Frank Rowand Cc: DTML , Michal Marek , Arnd Bergmann , Linux Kbuild mailing list , Linux Kernel Mailing List , Maxime Ripard , cyril@debamax.com, Geert Uytterhoeven , linux-arm-kernel References: <20210125105757.661240-1-uwe@kleine-koenig.org> <9d9bb0f6-d4f4-b1b9-a4c4-786987578085@kleine-koenig.org> <5e552b57-4e8b-6774-577d-4fa7a8d440ba@gmail.com> From: Frank Rowand Message-ID: <98217e0b-e937-f5b3-fa16-57c79b6ae3f6@gmail.com> Date: Tue, 26 Jan 2021 12:26:14 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <5e552b57-4e8b-6774-577d-4fa7a8d440ba@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Uwe, On 1/26/21 12:03 PM, Frank Rowand wrote: > +frank > > On 1/26/21 1:20 AM, Uwe Kleine-König wrote: >> Hello Masahiro, >> >> On 1/25/21 10:53 PM, Masahiro Yamada wrote: >>> On Mon, Jan 25, 2021 at 8:07 PM Uwe Kleine-König wrote: >>>> >>>> Adding the -@ switch to dtc results in the binary devicetrees containing >>>> a list of symbolic references and their paths. This is necessary to >>>> apply device tree overlays e.g. on Raspberry Pi as described on >>>> https://www.raspberrypi.org/documentation/configuration/device-tree.md. >>>> >>>> Obviously the downside of this change is an increas of the size of the >>>> generated dtbs, for an arm out-of-tree build (multi_v7_defconfig): >>>> >>>>          $ du -s arch/arm/boot/dts* >>>>          101380  arch/arm/boot/dts-pre >>>>          114308  arch/arm/boot/dts-post >>>> >>>> so this is in average an increase of 12.8% in size. >>>> >>>> Signed-off-by: Uwe Kleine-König >>> >>> >>> (CCing DT ML.) >> >> makes sense, thanks. >> >>> https://www.spinics.net/lists/linux-kbuild/msg27904.html >>> >>> See Rob's comment: >>> >>> "We've already rejected doing that. Turning on '-@' can grow the dtb >>> size by a significant amount which could be problematic for some >>> boards." >> >> The patch was created after some conversation on irc which continued >> after I sent the patch. I added the participating parties to Cc:. Unfortunately I have not been on irc recently (now rectified). Do you perchance have a copy of the irc conversation that you can send me? (No need to edit out unrelated messages, a simple cut and paste from the start of the conversation to the end is fine.) -Frank >> >> The (relevant) followups were: >> >> Geert suggested to always generate the symbols and provide a way to >> strip the symbols for installation if and when they are not needed. >> >> Rob said: "I'm less concerned with the size increases, but rather that >> labels go from purely source syntax to an ABI. I'd rather see some >> decision as to which labels are enabled or not." >> >> And then I learned with hints from Rob and Geert that symbols are not >> really necessary for overlays, you just cannot use named labels. But >> using >> >>     target-path = "/soc/i2c@23473245"; >> >> or >> >>     target = <&{/soc/i2c@23473245}>; >> >> instead of >> >>     target = <&i2c1>; >> >> works fine. (And if you need to add a phandle the &{/path/to/node} >> construct should work, too (but I didn't test).) Using labels is a tad nicer, but the problem I wanted to address with my patch now has a known different solution. >> >> Best regards >> Uwe >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >> >