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[2003:f6:5f00:7808::1b9]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-3a073cc4025sm17070285f8f.56.2025.04.30.04.56.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Apr 2025 04:56:24 -0700 (PDT) From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= To: linux-pwm@vger.kernel.org Cc: David Lechner , Kent Gibson , linux-kernel@vger.kernel.org Subject: [PATCH v7 3/4] pwm: Formally describe the procedure used to pick a hardware waveform setting Date: Wed, 30 Apr 2025 13:56:00 +0200 Message-ID: X-Mailer: git-send-email 2.47.2 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Developer-Signature: v=1; a=openpgp-sha256; l=2752; i=u.kleine-koenig@baylibre.com; h=from:subject:message-id; bh=RjoEXSIkY3DqTEk4/M+XxiagMUMOfWsaQZWgGc6PuWc=; b=owGbwMvMwMXY3/A7olbonx/jabUkhgwh/htfS9ZlvdrfbJkx37ufs2/D9FXxGzJzPIP6srx5k 3Zk777fyWjMwsDIxSArpshi37gm06pKLrJz7b/LMINYmUCmMHBxCsBEGrs5GFY+VLOcGVGw9/6k 9o18nTYnuQu1c9rUBaZa/Dy6Tr063XLlEkWDZfzFk2Rkvr0U7ZRMeO/dqL7W9fLH91crg8WmnPx WLWym/e1/dLHujujGFNbAT4FrZ8e2RGRsf+S4sye12orTOrb9tOc8iW13jHRjp3zeH7jGL183z2 HTpI0VgYk9rjOPJxo2+b1NN3gf1zitoWyZ3/NXtUE2Xpxn+Xc/dbT87mVxNqXbf8HKW27dkXdn3 BEMOFW/nz1u06+Tzu53rs/K4X3D68wSZiMlvr/67uGAfrn6eXJtqtLKEvVl35l+3S6q9pik8tHl cdIZrmW3Q3U1wp+faVrHVBdh+OHayQvrIn99Vra702IMAA== X-Developer-Key: i=u.kleine-koenig@baylibre.com; a=openpgp; fpr=0D2511F322BFAB1C1580266BE2DCDD9132669BD6 Content-Transfer-Encoding: quoted-printable This serves as specification for both, PWM consumers and the respective callback for lowlevel drivers. Signed-off-by: Uwe Kleine-K=C3=B6nig --- drivers/pwm/core.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c index 5cf64b3a4cdf..4d842c692194 100644 --- a/drivers/pwm/core.c +++ b/drivers/pwm/core.c @@ -231,7 +231,9 @@ static int __pwm_write_waveform(struct pwm_chip *chip, = struct pwm_device *pwm, c * * Usually all values passed in @wf are rounded down to the nearest possib= le * value (in the order period_length_ns, duty_length_ns and then - * duty_offset_ns). Only if this isn't possible, a value might grow. + * duty_offset_ns). Only if this isn't possible, a value might grow. See t= he + * documentation for pwm_set_waveform_might_sleep() for a more formal + * description. * * Returns: 0 on success, 1 if at least one value had to be rounded up or a * negative errno. @@ -411,6 +413,26 @@ static int __pwm_set_waveform(struct pwm_device *pwm, * possible/needed. In the above example requesting .period_length_ns =3D = 94 and * @exact =3D true, you get the hardware configured with period =3D 93.5 n= s. * + * Let C be the set of possible hardware configurations for a given PWM de= vice, + * consisting of tuples (p, d, o) where p is the period length, d is the d= uty + * length and o the duty offset. + * + * The following algorithm is implemented to pick the hardware setting + * (p, d, o) =E2=88=88 C for a given request (p', d', o') with @exact =3D = false:: + * + * p =3D max( { =E1=B9=97 | =E2=88=83 =E1=B8=8B, =C8=AF : (=E1=B9=97, = =E1=B8=8B, =C8=AF) =E2=88=88 C =E2=88=A7 =E1=B9=97 =E2=89=A4 p' } =E2=88=AA= { min({ =E1=B9=97 | =E2=88=83 =E1=B8=8B, =C8=AF : (=E1=B9=97, =E1=B8=8B, = =C8=AF) =E2=88=88 C }) }) + * d =3D max( { =E1=B8=8B | =E2=88=83 =C8=AF : (p, =E1=B8=8B, =C8=AF) = =E2=88=88 C =E2=88=A7 =E1=B8=8B =E2=89=A4 d' } =E2=88=AA { min({ =E1=B8=8B = | =E2=88=83 =C8=AF : (p, =E1=B8=8B, =C8=AF) =E2=88=88 C }) }) + * o =3D max( { =C8=AF | (p, d, =C8=AF) =E2=88=88 C =E2=88=A7 =C8=AF =E2= =89=A4 o' } =E2=88=AA { min({ =C8=AF | (p, d, =C8=AF) =E2=88=88 C }) }) + * + * In words: The chosen period length is the maximal possible period lengt= h not + * bigger than the requested period length and if that doesn't exist, the + * minimal period length. The chosen duty length is the maximal possible d= uty + * length that is compatible with the chosen period length and isn't bigge= r than + * the requested duty length. Again if such a value doesn't exist, the min= imal + * duty length compatible with the chosen period is picked. After that the= duty + * offset compatible with the chosen period and duty length is chosen in t= he + * same way. + * * Returns: 0 on success, -EDOM if setting failed due to the exact wavefor= m not * being possible (if @exact), or a different negative errno on failure. * Context: May sleep. --=20 2.47.2