Messages in this thread | | | Date | Fri, 13 Jan 2023 10:57:39 -0600 | Subject | Re: [PATCH 2/2] regmap: sdw: Remove 8-bit value size restriction | From | Pierre-Louis Bossart <> |
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On 1/13/23 05:02, Charles Keepax wrote: > On Thu, Jan 12, 2023 at 02:19:29PM -0600, Pierre-Louis Bossart wrote: >> On 1/12/23 13:50, Mark Brown wrote: >>> On Thu, Jan 12, 2023 at 12:43:46PM -0600, Pierre-Louis Bossart wrote: >>>> On 1/12/23 12:14, Mark Brown wrote: >>> >>>>> The regmap gather_write() operation allows the bus to take two buffers, >>>>> one for the register and one for the value, rather than requiring the >>>>> core combine everything into a single buffer (mainly useful for large >>>>> transfers like firmware downloads). >>> >>>> Right, but that's not supported in SoundWire. sdw_nwrite() will only >>>> work with consecutive addresses - and the auto-increment is handled in >>>> software, not hardware. >>> >>> No, that's exactly what this is for. It's for the *register address* >>> being in a separate buffer, the data is then a sequence of consecutive >>> register values.> >>>> What's suggested here is to use the first element of reg_buf, which begs >>>> the question how different this is from a regular write. If there was a >>>> discontinuity in reg_buf then this wouldn't work at all. >>> >>> reg_buf contains the address of exactly one register. >> >> So what's the difference with a plain write() of N data? > > There are two back end interfaces in regmap, the reg_write/read > and the plain write/read. Both have currently have some > limitations when dealing with SoundWire. > > The reg_write/reg_read can only deal with a single register > at a time, which is really far from ideal, since it means > all transactions will be broken up into individual registers > at the regmap level, mostly depriving the SoundWire side > of the opportunity to do things like a BRA transfer if it > deems that suitable. And denying users the ability to use the > regmap_raw_read/write API at all. > > The write/read interface allows us to pass the full transaction > through, but does have the downside it copies the address around > a bit more and does some pointless endian swaps on big endian > systems. This interface is generally used by buses like I2C/SPI > where there is no actual concept of a register address only a > buffer of bytes to be sent/read, thus prefers to pass a single > working buffer if it sensibly can. I went with this solution > because it enables all the functionality and the downside is > fairly minimal, apart from looking a little clunky as you note.
The change from reg_write/read_reg to write/read seems ok, what I was asking about was the gather_write.
+ .write = regmap_sdw_write, + .gather_write = regmap_sdw_gather_write, + .read = regmap_sdw_read,
what happens if you only have .write and .read? What does the .gather_write help with if you only use only address?
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