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Date: Tue, 13 Jun 2017 09:18:55 -0300
From: Mauro Carvalho Chehab <mchehab@...pensource.com>
To: <Yasunari.Takiguchi@...y.com>
Cc: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
<linux-media@...r.kernel.org>, <tbird20d@...il.com>,
<frowand.list@...il.com>,
Masayuki Yamamoto <Masayuki.Yamamoto@...y.com>,
Hideki Nozawa <Hideki.Nozawa@...y.com>,
"Kota Yonezawa" <Kota.Yonezawa@...y.com>,
Toshihiko Matsumoto <Toshihiko.Matsumoto@...y.com>,
Satoshi Watanabe <Satoshi.C.Watanabe@...y.com>
Subject: Re: [PATCH v2 04/15] [media] cxd2880: Add math functions for the
driver
Em Fri, 14 Apr 2017 11:22:37 +0900
<Yasunari.Takiguchi@...y.com> escreveu:
> From: Yasunari Takiguchi <Yasunari.Takiguchi@...y.com>
>
> Provide some math support functions (fixed-point log functions)
> for the Sony CXD2880 DVB-T2/T tuner + demodulator driver.
No need. The Kernel already provide log functions. You should use the
existing ones, instead of reinventing the wheel. The log2 functions
are at:
include/linux/log2.h
We also have both log2 and log10 functions at:
drivers/media/dvb-core/dvb_math.h
That should likely what you want.
>
> Signed-off-by: Yasunari Takiguchi <Yasunari.Takiguchi@...y.com>
> Signed-off-by: Masayuki Yamamoto <Masayuki.Yamamoto@...y.com>
> Signed-off-by: Hideki Nozawa <Hideki.Nozawa@...y.com>
> Signed-off-by: Kota Yonezawa <Kota.Yonezawa@...y.com>
> Signed-off-by: Toshihiko Matsumoto <Toshihiko.Matsumoto@...y.com>
> Signed-off-by: Satoshi Watanabe <Satoshi.C.Watanabe@...y.com>
> ---
> drivers/media/dvb-frontends/cxd2880/cxd2880_math.c | 89 ++++++++++++++++++++++
> drivers/media/dvb-frontends/cxd2880/cxd2880_math.h | 40 ++++++++++
> 2 files changed, 129 insertions(+)
> create mode 100644 drivers/media/dvb-frontends/cxd2880/cxd2880_math.c
> create mode 100644 drivers/media/dvb-frontends/cxd2880/cxd2880_math.h
>
> diff --git a/drivers/media/dvb-frontends/cxd2880/cxd2880_math.c b/drivers/media/dvb-frontends/cxd2880/cxd2880_math.c
> new file mode 100644
> index 000000000000..434c827898ff
> --- /dev/null
> +++ b/drivers/media/dvb-frontends/cxd2880/cxd2880_math.c
> @@ -0,0 +1,89 @@
> +/*
> + * cxd2880_math.c
> + * Sony CXD2880 DVB-T2/T tuner + demodulator driver
> + * mathmatics functions
> + *
> + * Copyright (C) 2016, 2017 Sony Semiconductor Solutions Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; version 2 of the License.
> + *
> + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
> + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
> + * NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
> + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
> + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
> + * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
> + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#include "cxd2880_math.h"
> +
> +#define MAX_BIT_PRECISION 5
> +#define FRAC_BITMASK 0x1F
> +#define LOG2_10_100X 332
> +#define LOG2_E_100X 144
> +
> +static const u8 log2_look_up[] = {
> + 0, 4,
> + 9, 13,
> + 17, 21,
> + 25, 29,
> + 32, 36,
> + 39, 43,
> + 46, 49,
> + 52, 55,
> + 58, 61,
> + 64, 67,
> + 70, 73,
> + 75, 78,
> + 81, 83,
> + 86, 88,
> + 91, 93,
> + 95, 98
> +};
> +
> +u32 cxd2880_math_log2(u32 x)
> +{
> + u8 count = 0;
> + u8 index = 0;
> + u32 xval = x;
> +
> + for (x >>= 1; x > 0; x >>= 1)
> + count++;
> +
> + x = count * 100;
> +
> + if (count > 0) {
> + if (count <= MAX_BIT_PRECISION) {
> + index =
> + (u8)(xval << (MAX_BIT_PRECISION - count)) &
> + FRAC_BITMASK;
> + x += log2_look_up[index];
> + } else {
> + index =
> + (u8)(xval >> (count - MAX_BIT_PRECISION)) &
> + FRAC_BITMASK;
> + x += log2_look_up[index];
> + }
> + }
> +
> + return x;
> +}
> +
> +u32 cxd2880_math_log10(u32 x)
> +{
> + return ((100 * cxd2880_math_log2(x) + LOG2_10_100X / 2) / LOG2_10_100X);
> +}
> +
> +u32 cxd2880_math_log(u32 x)
> +{
> + return ((100 * cxd2880_math_log2(x) + LOG2_E_100X / 2) / LOG2_E_100X);
> +}
> diff --git a/drivers/media/dvb-frontends/cxd2880/cxd2880_math.h b/drivers/media/dvb-frontends/cxd2880/cxd2880_math.h
> new file mode 100644
> index 000000000000..94211835a4ad
> --- /dev/null
> +++ b/drivers/media/dvb-frontends/cxd2880/cxd2880_math.h
> @@ -0,0 +1,40 @@
> +/*
> + * cxd2880_math.h
> + * Sony CXD2880 DVB-T2/T tuner + demodulator driver
> + * mathmatics definitions
> + *
> + * Copyright (C) 2016, 2017 Sony Semiconductor Solutions Corporation
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; version 2 of the License.
> + *
> + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
> + * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN
> + * NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
> + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
> + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
> + * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
> + * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
> + * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +
> +#ifndef CXD2880_MATH_H_
> +#define CXD2880_MATH_H_
> +
> +#include "cxd2880_common.h"
> +
> +u32 cxd2880_math_log2(u32 x);
> +u32 cxd2880_math_log10(u32 x);
> +u32 cxd2880_math_log(u32 x);
> +
> +#ifndef min
> +#define min(a, b) (((a) < (b)) ? (a) : (b))
> +#endif
We also have min() macro at the Kernel.
> +
> +#endif
Thanks,
Mauro
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