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Thu, 28 Feb 2019 06:54:31 -0600 Received: from [10.1.3.6] (ileax41-snat.itg.ti.com [10.172.224.153]) by dlep33.itg.ti.com (8.14.3/8.13.8) with ESMTP id x1SCsUvY004054; Thu, 28 Feb 2019 06:54:30 -0600 Subject: Re: hdmi-codec: modifying params in hw_params() callback To: Russell King - ARM Linux admin , Liam Girdwood , Mark Brown CC: , , References: <20190228121516.swd3vweisgcxlvld@shell.armlinux.org.uk> From: Jyri Sarha Openpgp: preference=signencrypt Autocrypt: addr=jsarha@ti.com; prefer-encrypt=mutual; keydata= mQINBFbdWt8BEADnCIkQrHIvAmuDcDzp1h2pO9s22nacEffl0ZyzIS//ruiwjMfSnuzhhB33 fNEWzMjm7eqoUBi1BUAQIReS6won0cXIEXFg9nDYQ3wNTPyh+VRjBvlb/gRJlf4MQnJDTGDP S5i63HxYtOfjPMSsUSu8NvhbzayNkN5YKspJDu1cK5toRtyUn1bMzUSKDHfwpdmuCDgXZSj2 t+z+c6u7yx99/j4m9t0SVlaMt00p1vJJ3HJ2Pkm3IImWvtIfvCmxnOsK8hmwgNQY6PYK1Idk puSRjMIGLqjZo071Z6dyDe08zv6DWL1fMoOYbAk/H4elYBaqEsdhUlDCJxZURcheQUnOMYXo /kg+7TP6RqjcyXoGgqjfkqlf3hYKmyNMq0FaYmUAfeqCWGOOy3PPxR/IiACezs8mMya1XcIK Hk/5JAGuwsqT80bvDFAB2XfnF+fNIie/n5SUHHejJBxngb9lFE90BsSfdcVwzNJ9gVf/TOJc qJEHuUx0WPi0taO7hw9+jXV8KTHp6CQPmDSikEIlW7/tJmVDBXQx8n4RMUk4VzjE9Y/m9kHE UVJ0bJYzMqECMTAP6KgzgkQCD7n8OzswC18PrK69ByGFpcm664uCAa8YiMuX92MnesKMiYPQ z1rvR5riXZdplziIRjFRX+68fvhPverrvjNVmzz0bAFwfVjBsQARAQABtBpKeXJpIFNhcmhh IDxqc2FyaGFAdGkuY29tPokCOAQTAQIAIgUCVt1a3wIbAwYLCQgHAwIGFQgCCQoLBBYCAwEC HgECF4AACgkQkDazUNfWGUEVVhAAmFL/21tUhZECrDrP9FWuAUuDvg+1CgrrqBj7ZxKtMaiz qTcZwZdggp8bKlFaNrmsyrBsuPlAk99f7ToxufqbV5l/lAT3DdIkjb4nwN4rJkxqSU3PaUnh mDMKIAp6bo1N9L+h82LE6CjI89W4ydQp5i+cOeD/kbdxbHHvxgNwrv5x4gg1JvEQLVnUSHva R2kx7u2rlnq7OOyh9vU0MUq7U5enNNqdBjjBTeaOwa5xb3S2Cc9dR10mpFiy+jSSkuFOjPpc fLfr/s03NGqbZ4aXvZCGjCw4jclpTJkuWPKO+Gb+a/3oJ4qpGN9pJ+48n2Tx9MdSrR4aaXHi EYMrbYQz9ICJ5V80P5+yCY5PzCvqpkizP6vtKvRSi8itzsglauMZGu6GwGraMJNBgu5u+HIZ nfRtJO1AAiwuupOHxe1nH05c0zBJaEP4xJHyeyDsMDh+ThwbGwQmAkrLJZtOd3rTmqlJXnuj sfgQlFyC68t1YoMHukz9LHzg02xxBCaLb0KjslfwuDUTPrWtcDL1a5hccksrkHx7k9crVFA1 o6XWsOPGKRHOGvYyo3TU3CRygXysO41UnGG40Q3B5R8RMwRHV925LOQIwEGF/6Os8MLgFXCb Lv3iJtan+PBdqO1Bv3u2fXUMbYgQ3v7jHctB8nHphwSwnHuGN7FAmto+SxzotE25Ag0EVt1a 3wEQAMHwOgNaIidGN8UqhSJJWDEfF/SPSCrsd3WsJklanbDlUCB3WFP2EB4k03JroIRvs7/V VMyITLQvPoKgaECbDS5U20r/Po/tmaAOEgC7m1VaWJUUEXhjYQIw7t/tSdWlo5XxZIcO4LwO Kf0S4BPrQux6hDLIFL8RkDH/8lKKc44ZnSLoF1gyjc5PUt6iwgGJRRkOD8gGxCv1RcUsu1xU U9lHBxdWdPmMwyXiyui1Vx7VJJyD55mqc7+qGrpDHG9yh3pUm2IWp7jVt/qw9+OE9dVwwhP9 GV2RmBpDmB3oSFpk7lNvLJ11VPixl+9PpmRlozMBO00wA1W017EpDHgOm8XGkq++3wsFNOmx 6p631T2WuIthdCSlZ2kY32nGITWn4d8L9plgb4HnDX6smrMTy1VHVYX9vsHXzbqffDszQrHS wFo5ygKhbGNXO15Ses1r7Cs/XAZk3PkFsL78eDBHbQd+MveApRB7IyfffIz7pW1R1ZmCrmAg Bn36AkDXJTgUwWqGyJMd+5GHEOg1UPjR5Koxa4zFhj1jp1Fybn1t4N11cmEmWh0aGgI/zsty g/qtGRnFEywBbzyrDEoV4ZJy2Q5pnZohVhpbhsyETeYKQrRnMk/dIPWg6AJx38Cl4P9PK1JX 8VK661BG8GXsXJ3uZbPSu6K0+FiJy09N4IW7CPJNABEBAAGJAh8EGAECAAkFAlbdWt8CGwwA CgkQkDazUNfWGUFOfRAA5K/z9DXVEl2kkuMuIWkgtuuLQ7ZwqgxGP3dMA5z3Iv/N+VNRGbaw oxf+ZkTbJHEE/dWclj1TDtpET/t6BJNLaldLtJ1PborQH+0jTmGbsquemKPgaHeSU8vYLCdc GV/Rz+3FN0/fRdmoq2+bIHght4T6KZJ6jsrnBhm7y6gzjMOiftH6M5GXPjU0/FsU09qsk/af jbwLETaea0mlWMrLd9FC2KfVITA/f/YG2gqtUUF9WlizidyctWJqSTZn08MdzaoPItIkRUTv 6Bv6rmFn0daWkHt23BLd0ZP7e7pON1rqNVljWjWQ/b/E/SzeETrehgiyDr8pP+CLlC+vSQxi XtjhWjt1ItFLXxb4/HLZbb/L4gYX7zbZ3NwkON6Ifn3VU7UwqxGLmKfUwu/mFV+DXif1cKSS v6vWkVQ6Go9jPsSMFxMXPA5317sZZk/v18TAkIiwFqda3/SSjwc3e8Y76/DwPvUQd36lEbva uBrUXDDhCoiZnjQaNz/J+o9iYjuMTpY1Wp+igjIretYr9+kLvGsoPo/kTPWyiuh/WiFU2d6J PMCGFGhodTS5qmQA6IOuazek1qSZIl475u3E2uG98AEX/kRhSzgpsbvADPEUPaz75uvlmOCX tv+Sye9QT4Z1QCh3lV/Zh4GlY5lt4MwYnqFCxroK/1LpkLgdyQ4rRVw= Message-ID: <421c1217-6ff6-6ca2-8169-db026284fb29@ti.com> Date: Thu, 28 Feb 2019 14:54:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190228121516.swd3vweisgcxlvld@shell.armlinux.org.uk> Content-Type: text/plain; charset="utf-8" Content-Language: en-GB Content-Transfer-Encoding: 8bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/02/2019 14:15, Russell King - ARM Linux admin wrote: > Hi all, > > While looking at hdmi-codec issues, I spotted this code: > > static int hdmi_codec_hw_params(struct snd_pcm_substream *substream, > struct snd_pcm_hw_params *params, > struct snd_soc_dai *dai) > { > ... > if (params_width(params) > 24) > params->msbits = 24; > > params->msbits is a parameter that is negotiated and refined by > libasound, and is part of the ALSA constraint system. The "Writing an > ALSA driver" documentation says about the hw_params callback: > > "This is called when the hardware parameter (``hw_params``) is set up > by the application, that is, once when the buffer size, the period > size, the format, etc. are defined for the pcm substream." > > which suggests we should only be reading the parameters, not writing > to them. > > What's more is that the msbits is a parameter that is refined with > userspace, so surely the above should be a declared constraint? > Certainly not a constraint. While HDMI can only pass up to 24-bit per sample audio the most (or at least the two I have worked with) encoders can take 32-bit wide (and probably wider) samples trough i2s. So the system can play 32-bit samples, just the 4 LSB is ignored. Actually there is very little difference between the case of playing 32-bit stereo audio with matching i2s bclk ratio, and playing 24-bit stereo audio with 64-bit bclk ratio. Especially when the 4 LSB is anyway ignored like in HDMI audio case. > Digging a bit deeper, ASoC passes a private copy of the params to each > codec - a copy is made, then fixups for TDM slots are applied, followed > by any topology fixups by the DAI link (be_hw_params_fixup) before the > codec driver's hw_params() callback is made. Afterwards, ASoC reads > back the rate, channels and physical (memory) width and stores them > in the codec's DAI structure. The msbits are not read. > > hdmi-codec also seems to do nothing with the msbits parameter other > than the above code. > > So, all in all, it seems that the above code limiting msbits is > redundant - nothing will read this modified value. Can we kill it? > It certainly looks that way, so yes. In any case struct snd_soc_dai_driver .playback.sig_bits = 24 should be all that is needed. Regards, Jyri -- Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki. Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki