Messages in this thread | | | Date | Tue, 30 Jul 2019 17:08:42 -0700 (PDT) | From | Paul Walmsley <> | Subject | Re: [PATCH 3/4] RISC-V: Support case insensitive ISA string parsing. |
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On Mon, 29 Jul 2019, Atish Patra wrote:
> The yaml document did not specify anything about all isa-strings has to > be lowercase unless I missed something. The two enum values are all > lowercase but the description says all ISA strings are documented in ISA > specification which describes the ISA strings to be case insensitive. > IMHO, this creates confusion resulting the patch.
If it's helpful in understanding my earlier comments, I don't think that your patches were "wrong," or anything like that. And you're right that the DT YAML binding does not unequivocally state that all future additions to the riscv,isa string must be in lowercase. But to be clear, the DT YAML schema defines exactly what is currently permissible for riscv,isa strings in kernel-oriented DT data, and right now, all of the permissible values are lowercase.
Good Linux kernel patches are driven by clear functional motivations. Like, "The current kernel crashes or doesn't support the hardware in situation X; thus we change the kernel to add feature or bugfix Y." And in the kernel, solutions that involve fewer lines of code are generally preferred to solutions that involve more lines of code - more bugs, more noise, etc.
Where these case-insensitivity parsing patches fall short, in my opinion, is that they don't have strong functional motivations. There's been a precedent for a few years now in the mainline kernel that the RISC-V ISA string is all lowercase. I've asked you and Anup for situations where that precedent isn't sufficient to handle functionality that's described in the RISC-V specification, or to phrase it differently, "what breaks if we don't make this change?" So far no one's been able to cite anything here. There's just a repeated appeal to authority to the section of the RISC-V specification that states that "[t]he ISA naming strings are case insensitive." As you can probably sense, this doesn't seem like a strong justification for changing the existing behavior. From a functional point of view, if case doesn't matter, why care if the DT data and kernel only support lowercase strings? An all-lowercase string should be functionally equivalent to an all-uppercase or mixed-case string. Since there's no functional point to the changes, why add more code to the kernel?
Later in your E-mail, it sounds like you ultimately agree with these basic conclusions. If that's so, I don't understand the amount of effort that you and Anup have put into pushing back here. There's nothing personal about these review comments. If there's some meta-problem here that's unrelated to the technical merit of the patches, please send a private E-mail. Otherwise, if you disagree with the functional conclusions in the previous paragraph, let's hash the issues out here.
> I am fine with dropping this patch if yaml clearly document the case > sensititve thing.
Great! If you still think so now, let's resolve this issue with a one-line patch to the DT YAML schema to note that riscv,isa DT string values should be all lowercase. Will you send a patch?
- Paul
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