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Wed, 25 Mar 2026 15:08:05 +0100 (CET) Message-ID: <1ca0acb2-18fb-449e-9a52-e73d9eebfb62@perex.cz> Date: Wed, 25 Mar 2026 15:08:04 +0100 Precedence: bulk X-Mailing-List: linux-sound@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: (re)use and (re)definition of snd_pcm_hw_params->fifo_size for 'jumpy DMA' To: =?UTF-8?Q?P=C3=A9ter_Ujfalusi?= , Takashi Iwai , Mark Brown , Liam Girdwood Cc: Linux-ALSA , "linux-sound@vger.kernel.org" , Kai Vehmanen , arun@asymptotic.io, wim.taymans@gmail.com References: <8fe7f61b-dae4-4ae6-aa96-7e604a37e624@linux.intel.com> <813612ea-f942-432f-9bf1-7b1ccfe59046@perex.cz> <6b129498-f130-44a0-a679-6fa1c639046e@linux.intel.com> <420a8205-6a95-4e8a-852e-f3094200e5b1@linux.intel.com> From: Jaroslav Kysela Content-Language: en-US Autocrypt: addr=perex@perex.cz; keydata= xsFNBFvNeCsBEACUu2ZgwoGXmVFGukNPWjA68/7eMWI7AvNHpekSGv3z42Iy4DGZabs2Jtvk ZeWulJmMOh9ktP9rVWYKL9H54gH5LSdxjYYTQpSCPzM37nisJaksC8XCwD4yTDR+VFCtB5z/ E7U0qujGhU5jDTne3dZpVv1QnYHlVHk4noKxLjvEQIdJWzsF6e2EMp4SLG/OXhdC9ZeNt5IU HQpcKgyIOUdq+44B4VCzAMniaNLKNAZkTQ6Hc0sz0jXdq+8ZpaoPEgLlt7IlztT/MUcH3ABD LwcFvCsuPLLmiczk6/38iIjqMtrN7/gP8nvZuvCValLyzlArtbHFH8v7qO8o/5KXX62acCZ4 aHXaUHk7ahr15VbOsaqUIFfNxpthxYFuWDu9u0lhvEef5tDWb/FX+TOa8iSLjNoe69vMCj1F srZ9x2gjbqS2NgGfpQPwwoBxG0YRf6ierZK3I6A15N0RY5/KSFCQvJOX0aW8TztisbmJvX54 GNGzWurrztj690XLp/clewmfIUS3CYFqKLErT4761BpiK5XWUB4oxYVwc+L8btk1GOCOBVsp 4xAVD2m7M+9YKitNiYM4RtFiXwqfLk1uUTEvsaFkC1vu3C9aVDn3KQrZ9M8MBh/f2c8VcKbN njxs6x6tOdF5IhUc2E+janDLPZIfWDjYJ6syHadicPiATruKvwARAQABzSBKYXJvc2xhdiBL eXNlbGEgPHBlcmV4QHBlcmV4LmN6PsLBjgQTAQgAOBYhBF7f7LZepM3UTvmsRTCsxHw/elMJ BQJbzXgrAhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEDCsxHw/elMJDGAP/ReIRiRw lSzijpsGF/AslLEljncG5tvb/xHwCxK5JawIpViwwyJss06/IAvdY5vn5AdfUfCl2J+OakaR VM/hdHjCYNu4bdBYZQBmEiKsPccZG2YFDRudEmiaoaJ1e8ZsiA3rSf4SiWWsbcBOYHr/unTf 4KQsdUHzPUt8Ffi9HrAFzI2wjjiyV5yUGp3x58ZypAIMcKFtA1aDwhA6YmQ6lb8/bC0LTC6l cAAS1tj7YF5nFfXsodCOKK5rKf5/QOF0OCD2Gy+mGLNQnq6S+kD+ujQfOLaUHeyfcNBEBxda nZID7gzd65bHUMAeWttZr3m5ESrlt2SaNBddbN7NVpVa/292cuwDCLw2j+fAZbiVOYyqMSY4 LaNqmfa0wJAv30BMKeRAovozJy62j0AnntqrvtDqqvuXgYirj2BEDxx0OhZVqlI8o5qB6rA5 Pfp2xKRE8Fw3mASYRDNad08JDhJgsR/N5JDGbh4+6sznOA5J63TJ+vCFGM37M5WXInrZJBM3 ABicmpClXn42zX3Gdf/GMM3SQBrIriBtB9iEHQcRG/F+kkGOY4QDi4BZxo45KraANGmCkDk0 +xLZVfWh8YOBep+x2Sf83up5IMmIZAtYnxr77VlMYHDWjnpFnfuja+fcnkuzvvy7AHJZUO1A aKexwcBjfTxtlX4BiNoK+MgrjYywzsFNBFvNeCsBEACb8FXFMOw1g+IGVicWVB+9AvOLOhqI FMhUuDWmlsnT8B/aLxcRVUTXoNgJpt0y0SpWD3eEJOkqjHuvHfk+VhKWDsg6vlNUmF1Ttvob 18rce0UH1s+wlE8YX8zFgODbtRx8h/BpykwnuWNTiotu9itlE83yOUbv/kHOPUz4Ul1+LoCf V2xXssYSEnNr+uUG6/xPnaTvKj+pC7YCl38Jd5PgxsP3omW2Pi9T3rDO6cztu6VvR9/vlQ8Z t0p+eeiGqQV3I+7k+S0J6TxMEHI8xmfYFcaVDlKeA5asxkqu5PDZm3Dzgb0XmFbVeakI0be8 +mS6s0Y4ATtn/D84PQo4bvYqTsqAAJkApEbHEIHPwRyaXjI7fq5BTXfUO+++UXlBCkiH8Sle 2a8IGI1aBzuL7G9suORQUlBCxy+0H7ugr2uku1e0S/3LhdfAQRUAQm+K7NfSljtGuL8RjXWQ f3B6Vs7vo+17jOU7tzviahgeRTcYBss3e264RkL62zdZyyArbVbK7uIU6utvv0eYqG9cni+o z7CAe7vMbb5KfNOAJ16+znlOFTieKGyFQBtByHkhh86BQNQn77aESJRQdXvo5YCGX3BuRUaQ zydmrgwauQTSnIhgLZPv5pphuKOmkzvlCDX+tmaCrNdNc+0geSAXNe4CqYQlSnJv6odbrQlD Qotm9QARAQABwsF2BBgBCAAgFiEEXt/stl6kzdRO+axFMKzEfD96UwkFAlvNeCsCGwwACgkQ MKzEfD96Uwlkjg/+MZVS4M/vBbIkH3byGId/MWPy13QdDzBvV0WBqfnr6n99lf7tKKp85bpB y7KRAPtXu+9WBzbbIe42sxmWJtDFIeT0HJxPn64l9a1btPnaILblE1mrfZYAxIOMk3UZA3PH uFdyhQDJbDGi3LklDhsJFTAhBZI5xMSnqhaMmWCL99OWwfyJn2omp8R+lBfAJZR31vW6wzsj ssOvKIbgBpV/o3oGyAofIXPYzhY+jhWgOYtiPw9bknu748K+kK3fk0OeEG6doO4leB7LuWig dmLZkcLlJzSE6UhEwHZ8WREOMIGJnMF51WcF0A3JUeKpYYEvSJNDEm7dRtpb0x/Y5HIfrg5/ qAKutAYPY7ClQLu5RHv5uqshiwyfGPaiE8Coyphvd5YbOlMm3mC/DbEstHG7zA89fN9gAzsJ 0TFL5lNz1s/fo+//ktlG9H28EHD8WOwkpibsngpvY+FKUGfJgIxpmdXVOkiORWQpndWyRIqw k8vz1gDNeG7HOIh46GnKIrQiUXVzAuUvM5vI9YaW3YRNTcn3pguQRt+Tl9Y6G+j+yvuLL173 m4zRUU6DOygmpQAVYSOJvKAJ07AhQGaWAAi5msM6BcTU4YGcpW7FHr6+xaFDlRHzf1lkvavX WoxP1IA1DFuBMeYMzfyi4qDWjXc+C51ZaQd39EulYMh+JVaWRoY= In-Reply-To: <420a8205-6a95-4e8a-852e-f3094200e5b1@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/25/26 14:28, Péter Ujfalusi wrote: > Looking at the PW code (spa/plugins/alsa/alsa-pcm.c) and I sort of > started to appreciate the 'headroom' term. > > I disagree that this is not about DMA or about burst since it is > precisely about that. It can be viewed as 'latency' but the latency is > reported via the delay and the delay fluctuates over time based on how > the DSP FIFO drains and fills. My point was that we should not use those terms for the structure members, because it's standard prefill / data fetch (put) granularity issue. DMA is just the concrete use. Describing both parameters seem like the best idea. > PW then probably can use these: > state->start_delay = hw_buffer_size; > state->headroom = hw_buffer_refill_step_size We don't use head/tail in the buffer variables for ALSA API. The headroom can be named just 'update_granularity' or 'update_step' or so. Also, start delay is not correct, too. Maybe 'prefill' or 'init_fill' says all. Or we can eventually try to be more consistent and use 'init_chunk' and 'step_chunk' to notify applications about the data transfer characteristics from the other (hw) side of the audio buffer. The chunk word is not used actually in the ALSA API, so developers should not mix that with other things like fifo or period. > and on start/xrun it might need to provide > state->start_delay + max(state->start_delay, state->headroom) > or to the distance that it is planning to wake up. It will end with 2 * prefill for your examples, because start_delay > headroom. It should be just prefill + step. Also, it seems that in SOF case, the queued "prefill" sample block is mandatory for internal processing, otherwise xrun will happen, or no ? Jaroslav -- Jaroslav Kysela Linux Sound Maintainer; ALSA Project; Red Hat, Inc.