Messages in this thread | | | Date | Thu, 20 Mar 2014 20:05:39 +0100 | From | Lars-Peter Clausen <> | Subject | Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux |
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On 03/20/2014 07:36 PM, Mark Brown wrote: > On Thu, Mar 20, 2014 at 12:20:17PM -0600, Stephen Warren wrote: >> On 03/20/2014 05:48 AM, Mark Brown wrote: >>> On Wed, Mar 19, 2014 at 04:44:00PM -0700, Arun Shamanna Lakshmi wrote: > >>>> If each bit of a 32 bit register maps to an input of a mux, then with >>>> the current 'soc_enum' structure we cannot have more than 64 inputs >>>> for the mux (because of reg and reg2 only). > >>> What makes you say that? We currently have devices in mainline which >>> have well over 32 inputs to muxes. > >> I think their register layout is different. > >> I found a number of large muxes where the register stores a 'integer' >> indicating which mux input to select, e.g. Arizona, WM2200, etc. In this >> case, an N-bit register could support up to 2^N inputs. > >> However, the registers in the Tegra AHUB use 1 bit position per input, >> and require you to set one single bit at a time. Hence, an N bit >> register (or string of registers) can support up to N inputs. In more >> recent Tegra chips, we have at least >32 inputs and I think Arun was >> saying even >64 inputs. That requires 2 or 3 or more .reg fields in >> struct soc_enum. > > Right, that was my guess too (the mail wasn't terribly clear with the > formatting, references to unpublished documents and so on) but that's > not a straight mux, it's a value mux, and the limit with the current > code is much lower on 32 bit systems (like at least some of the K1s) > since muxes only use one of the current register fields.
It might make sense to add special code for supported muxes with a one-hot encoding instead of using a value mux. Having an large array where each entry is just 1<<n is a bit ugly in my opinion, especially if the value needs to be able to be larger than 2**64. But anyway the patch that modifies the soc_enum struct should also add the code that makes use of the new struct layout.
- Lars
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