On Mon, Oct 23, 2023 at 02:00:00PM -0300, Daniel Henrique Barboza wrote: > > > On 10/23/23 05:16, Andrew Jones wrote: > > On Fri, Oct 20, 2023 at 07:39:48PM -0300, Daniel Henrique Barboza wrote: > > > The TCG emulation implements all the extensions described in the > > > RVA22U64 profile, both mandatory and optional. The mandatory extensions > > > will be enabled via the profile flag. We'll leave the optional > > > extensions to be enabled by hand. > > > > > > Given that this is the first profile we're implementing in TCG we'll > > > need some ground work first: > > > > > > - all profiles declared in riscv_profiles[] will be exposed to users. > > > TCG is the main accelerator we're considering when adding profile > > > support in QEMU, so for now it's safe to assume that all profiles in > > > riscv_profiles[] will be relevant to TCG; > > > > > > - we'll not support user profile settings for vendor CPUs. The flags > > > will still be exposed but users won't be able to change them. The idea > > > is that vendor CPUs in the future can enable profiles internally in > > > their cpu_init() functions, showing to the external world that the CPU > > > supports a certain profile. But users won't be able to enable/disable > > > it; > > > > > > - Setting a profile to 'true' means 'enable all mandatory extensions of > > > this profile, setting it to 'false' means disabling all its mandatory > > > extensions. Disabling a profile is discouraged for regular use and will > > > issue an user warning. User choices for individual extensions will take > > > precedence, i.e. enabling a profile will not enable extensions that the > > > user set to 'false', and vice-versa. This will make us independent of > > > left-to-right ordering in the QEMU command line, i.e. the following QEMU > > > command lines: > > > > > > -cpu rv64,zicbom=false,rva22u64=true,Zifencei=false > > > -cpu rv64,zicbom=false,Zifencei=false,rva22u64=true > > > -cpu rv64,rva22u64=true,zicbom=false,Zifencei=false > > > > > > They mean the same thing: "enable all mandatory extensions of the > > > rva22u64 profile while keeping zicbom and Zifencei disabled". > > > > Hmm, I'm not sure I agree with special-casing profiles like this. I think > > the left-to-right processing should be consistent for all. I'm also not > > sure we should always warn when disabling a profile. For example, if a > > user does > > > > -cpu rv64,rva22u64=true,rva22u64=false > > > > then they'll get a warning, even though all they're doing is restoring the > > cpu model. While that looks like an odd thing to do, a script may be > > adding the rva22u64=true and the rva22u64=false is the user input which > > undoes what the script did. > > QEMU options do not work with a "the user enabled then disabled the same > option, > thus it'll count as nothing happened" logic. The last instance of the option > will > overwrite all previous instances. In the example you mentioned above the user > would > disable all mandatory extensions of rva22u64 in the CPU, doesn't matter if the > same profile was enabled beforehand.
Yup, I'm aware, but I keep thinking that we'll only be using profiles with a base cpu type. If you start with nothing (a base) and then add a profile and take the same one away, you shouldn't be taking away anything else. I agree that if you use a profile on some cpu type that already enabled a bunch of stuff itself, then disabling a profile would potentially remove some of those too, but mixing cpu types that have their own extensions and profiles seems like a great way to confuse oneself as to what extensions will be present. IOW, we should be adding a base cpu type at the same time we're adding these profiles. > > Sure, the can put code in place to make this happen, but then this would make > profiles act different than regular extensions. "-cpu rv64,zicbom=true -cpu > rv64,zicbom=false" > will disable zicbom, it will not preserve the original 'zicbom' rv64 default. > If > we're going to keep left-to-right ordering consistent, this behavior should > also > be consistent as well. It will be consistent if we always override whatever was on the left with what's on the right, which means with -cpu rv64,rva22u64=true -cpu rv64,zicbom=false zicbom will be disabled, but with -cpu rv64,zicbom=false -cpu rv64,rva22u64=true it will be enabled. The same goes if the properties are given to the same -cpu parameter. > > > As for warnings, I agree that we'll throw warnings even when nothing of > notice happened. > For example: > > -cpu rv64,rva22u64=false -cpu rv64,rva22u64=true > > This will throw a warning even though the user ended up enabling the extension > in the end. > > > We can fix it by postponing warnings to realize(). > > > > > > As far as warnings go, it'd be nice to warn when mandatory profile > > extensions are disabled from an enabled profile. Doing that might be > > useful for debug, but users which do it without being aware they're > > "breaking" the profile may learn from that warning. Note, the warning > > should only come when the profile is actually enabled and when the > > extension would actually be disabled, i.e. > > > > -cpu rv64,rva22u64=true,c=off > > > > should warn > > > > -cpu rv64,c=off,rva22u64=true > > > > should not warn (rva22u64 overrides c=off since it's to the right) > > > > -cpu rv64,rva22u64=true,rva22u64=false,c=off > > > > should not warn (rva22u64 is not enabled) > > Ack for all the above. > > > > > And, > > > > -cpu rv64,rva22u64=true,rva24u64=false > > > > should warn for each extension which is mandatory in both profiles. > > The way I'm imagining this happening is to cycle through all profiles during > realize(), > see which ones are enabled, and then warn if the user disabled their mandatory > extensions. In this example we would warn for all rva22 mandatory extensions > that were disabled because we disabled rva24, but we won't emit any warnings > for > rva24 mandatory extensions given that the profile is marked as disabled. Yup, sounds good. Thanks, drew