From: Geert Uytterhoeven <geert+renesas@glider.be> To: Mark Brown <broonie@kernel.org> Cc: Chris Brandt <chris.brandt@renesas.com>, linux-spi@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-sh@vger.kernel.org, Geert Uytterhoeven <geert+renesas@glider.be> Subject: [PATCH 4/8] spi: rspi: Increase bit rate accuracy on RZ/A Date: Mon, 08 Jun 2020 09:59:36 +0000 [thread overview] Message-ID: <20200608095940.30516-5-geert+renesas@glider.be> (raw) In-Reply-To: <20200608095940.30516-1-geert+renesas@glider.be> rspi_rz_set_config_register() favors high values of "brdv" over high values of "spbr". As "brdv" is not a plain divider, but controls a power-of-two divider, this may cause the selection of non-optimal divider values. E.g. on RSK+RZA1, when 3.8 MHz is requested, the actual configured bit rate is 2.08 MHz (spbr = 1, brdv = 3), while 3.7 MHz would be possible (spbr = 8, brdv = 0). Fix this by only resorting to higher "brdv" values when really needed. This makes the driver always pick optimal divider values on RZ/A. Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> --- drivers/spi/spi-rspi.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 450a42ec2141a895..ad4ac867170b101a 100644 --- a/drivers/spi/spi-rspi.c +++ b/drivers/spi/spi-rspi.c @@ -298,15 +298,13 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); clksrc = clk_get_rate(rspi->clk); - while (brdv < 3) { - if (rspi->speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */ - break; + spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; + while (spbr > 255 && brdv < 3) { brdv++; - clksrc /= 2; + spbr = DIV_ROUND_UP(spbr + 1, 2) - 1; } /* Sets transfer bit rate */ - spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); rspi->spcmd |= SPCMD_BRDV(brdv); -- 2.17.1
WARNING: multiple messages have this Message-ID (diff)
From: Geert Uytterhoeven <geert+renesas@glider.be> To: Mark Brown <broonie@kernel.org> Cc: Chris Brandt <chris.brandt@renesas.com>, linux-spi@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-sh@vger.kernel.org, Geert Uytterhoeven <geert+renesas@glider.be> Subject: [PATCH 4/8] spi: rspi: Increase bit rate accuracy on RZ/A Date: Mon, 8 Jun 2020 11:59:36 +0200 [thread overview] Message-ID: <20200608095940.30516-5-geert+renesas@glider.be> (raw) In-Reply-To: <20200608095940.30516-1-geert+renesas@glider.be> rspi_rz_set_config_register() favors high values of "brdv" over high values of "spbr". As "brdv" is not a plain divider, but controls a power-of-two divider, this may cause the selection of non-optimal divider values. E.g. on RSK+RZA1, when 3.8 MHz is requested, the actual configured bit rate is 2.08 MHz (spbr = 1, brdv = 3), while 3.7 MHz would be possible (spbr = 8, brdv = 0). Fix this by only resorting to higher "brdv" values when really needed. This makes the driver always pick optimal divider values on RZ/A. Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> --- drivers/spi/spi-rspi.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 450a42ec2141a895..ad4ac867170b101a 100644 --- a/drivers/spi/spi-rspi.c +++ b/drivers/spi/spi-rspi.c @@ -298,15 +298,13 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); clksrc = clk_get_rate(rspi->clk); - while (brdv < 3) { - if (rspi->speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */ - break; + spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; + while (spbr > 255 && brdv < 3) { brdv++; - clksrc /= 2; + spbr = DIV_ROUND_UP(spbr + 1, 2) - 1; } /* Sets transfer bit rate */ - spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); rspi->spcmd |= SPCMD_BRDV(brdv); -- 2.17.1
next prev parent reply other threads:[~2020-06-08 9:59 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-08 9:59 [PATCH 0/8] spi: rspi: Bit rate improvements Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 1/8] spi: rspi: Remove useless .set_config_register() check Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 2/8] spi: rspi: Use requested instead of maximum bit rate Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 3/8] spi: rspi: Clean up Bit Rate Division Setting handling Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven [this message] 2020-06-08 9:59 ` [PATCH 4/8] spi: rspi: Increase bit rate accuracy on RZ/A Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 5/8] spi: rspi: Increase bit rate range for RSPI on SH Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 6/8] spi: rspi: Increase bit rate range for QSPI Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 7/8] spi: rspi: Fill in spi_transfer.effective_speed_hz Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-08 9:59 ` [PATCH 8/8] spi: rspi: Fill in controller speed limits Geert Uytterhoeven 2020-06-08 9:59 ` Geert Uytterhoeven 2020-06-09 12:54 ` [PATCH 0/8] spi: rspi: Bit rate improvements Mark Brown 2020-06-09 12:54 ` Mark Brown
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