linux-kernel - Re: [PATCH 3/4] soundwire: SDCA: add helper macro to access controls

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Message-ID: <20200826085540.GY2639@vkoul-mobl>
Date:   Wed, 26 Aug 2020 14:25:40 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, gregkh@...uxfoundation.org,
        jank@...ence.com, srinivas.kandagatla@...aro.org,
        slawomir.blauciak@...el.com,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Hui Wang <hui.wang@...onical.com>,
        Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [PATCH 3/4] soundwire: SDCA: add helper macro to access controls

On 25-08-20, 12:16, Pierre-Louis Bossart wrote:
> The upcoming SDCA (SoundWire Device Class Audio) specification defines
> a hierarchical encoding to interface with Class-defined capabilities.
> 
> The specification is not yet accessible to the general public but this
> information is released with explicit permission from the MIPI Board
> to avoid delays with SDCA support on Linux platforms.
> 
> A block of 64 MBytes of register addresses are allocated to SDCA
> controls, starting at address 0x40000000. The 26 LSBs which identify
> individual controls are set based on the following variables:
> 
> - Function Number. An SCDA device can be split in up to 8 independent
>   Functions. Each of these Functions is described in the SDCA
>   specification, e.g. Smart Amplifier, Smart Microphone, Simple
>   Microphone, Jack codec, HID, etc.
> 
> - Entity Number.  Within each Function,  an Entity is  an identifiable
>   block.  Up   to  127  Entities   are  connected  in   a  pre-defined
>   graph  (similar to  USB), with  Entity0 reserved  for Function-level
>   configurations.  In  contrast  to  USB, the  SDCA  spec  pre-defines
>   Function Types, topologies, and allowed  options, i.e. the degree of
>   freedom  is not  unlimited to  limit  the possibility  of errors  in
>   descriptors leading to software quirks.
> 
> - Control Selector. Within each Entity, the SDCA specification defines
>   48 controls such as Mute, Gain, AGC, etc, and 16 implementation
>   defined ones. Some Control Selectors might be used for low-level
>   platform setup, and other exposed to applications and users. Note
>   that the same Control Selector capability, e.g. Latency control,
>   might be located at different offsets in different entities, the
>   Control Selector mapping is Entity-specific.
> 
> - Control Number. Some Control Selectors allow channel-specific values
>   to be set, with up to 64 channels allowed. This is mostly used for
>   volume control.
> 
> - Current/Next values. Some Control Selectors are
>   'Dual-Ranked'. Software may either update the Current value directly
>   for immediate effect. Alternatively, software may write into the
>   'Next' values and update the SoundWire 1.2 'Commit Groups' register
>   to copy 'Next' values into 'Current' ones in a synchronized
>   manner. This is different from bank switching which is typically
>   used to change the bus configuration only.
> 
> - MBQ. the Multi-Byte Quantity bit is used to provide atomic updates
>   when accessing more that one byte, for example a 16-bit volume
>   control would be updated consistently, the intermediate values
>   mixing old MSB with new LSB are not applied.
> 
> These 6 parameters are used to build a 32-bit address to access the
> desired Controls. Because of address range, paging is required, but
> the most often used parameter values are placed in the lower 16 bits
> of the address. This helps to keep the paging registers constant while
> updating Controls for a specific Device/Function.
> 
> Reviewed-by: Rander Wang <rander.wang@...ux.intel.com>
> Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>
> Reviewed-by: Kai Vehmanen <kai.vehmanen@...ux.intel.com>
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
> ---
>  include/linux/soundwire/sdw_registers.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/include/linux/soundwire/sdw_registers.h b/include/linux/soundwire/sdw_registers.h
> index 5d3c271af7d1..906dadda7387 100644
> --- a/include/linux/soundwire/sdw_registers.h
> +++ b/include/linux/soundwire/sdw_registers.h
> @@ -305,4 +305,17 @@
>  #define SDW_CASC_PORT_MASK_INTSTAT3		1
>  #define SDW_CASC_PORT_REG_OFFSET_INTSTAT3	2
>  
> +/* v1.2 device - SDCA address mapping */

Can you please add description of bits used by each field here,
something like we have done for DevId

> +#define SDW_SDCA_CTL(fun, ent, ctl, ch)		(BIT(30) |			\
> +						 (((fun) & 0x7) << 22) |	\
> +						 (((ent) & 0x40) << 15) |	\
> +						 (((ent) & 0x3f) << 7) |	\
> +						 (((ctl) & 0x30) << 15) |	\
> +						 (((ctl) & 0x0f) << 3) |	\
> +						 (((ch) & 0x38) << 12) |	\
> +						 ((ch) & 0x07))

GENMASK() for the bitmaps here please. Also it would look very neat by
using FIELD_PREP() here, you can skip the bit shifts and they would be
done by FIELD_PREP() for you.

> -- 
> 2.25.1

-- 
~Vinod