From: Biju Das <biju.das.jz@bp.renesas.com>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Biju Das <biju.das.jz@bp.renesas.com>,
Wolfram Sang <wsa+renesas@sang-engineering.com>,
linux-mmc@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
Geert Uytterhoeven <geert+renesas@glider.be>,
Chris Paterson <Chris.Paterson2@renesas.com>,
Biju Das <biju.das@bp.renesas.com>,
Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@bp.renesas.com>
Subject: [PATCH v3] mmc: renesas_sdhi: Fix rounding errors
Date: Thu, 22 Sep 2022 09:55:11 +0100 [thread overview]
Message-ID: <20220922085511.1078256-1-biju.das.jz@bp.renesas.com> (raw)
Due to clk rounding errors on RZ/G2L platforms, it selects a clock source
with a lower clock rate compared to a higher one.
For eg:- (533333333 Hz / 4 * 4 = 533333332 Hz < 533333333 Hz).
This patch fixes this issue by adding a margin of (1/1024) higher to
the clock rate.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
---
v2->v3:
* Renamed the variable new_clock_margin->new_upper_limit in renesas_sdhi_clk_
update()
* Moved setting of new_upper_limit outside for loop.
* Updated the comment section to mention the rounding errors and merged with
existing comment out side the for loop.
* Updated commit description.
v1->v2:
* Add a comment explaining why margin is needed and set it to
that particular value.
---
drivers/mmc/host/renesas_sdhi_core.c | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/drivers/mmc/host/renesas_sdhi_core.c b/drivers/mmc/host/renesas_sdhi_core.c
index 6edbf5c161ab..45ec15ece1f5 100644
--- a/drivers/mmc/host/renesas_sdhi_core.c
+++ b/drivers/mmc/host/renesas_sdhi_core.c
@@ -128,6 +128,7 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
struct clk *ref_clk = priv->clk;
unsigned int freq, diff, best_freq = 0, diff_min = ~0;
unsigned int new_clock, clkh_shift = 0;
+ unsigned int new_upper_limit;
int i;
/*
@@ -153,10 +154,15 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
* greater than, new_clock. As we can divide by 1 << i for
* any i in [0, 9] we want the input clock to be as close as
* possible, but no greater than, new_clock << i.
+ *
+ * To fix rounding errors, eg:- (533333333 Hz / 4 * 4 = 533333332 Hz <
+ * 533333333 Hz) add an upper limit of 1/1024 rate higher to the clock
+ * rate.
*/
+ new_upper_limit = (new_clock << i) + ((new_clock << i) >> 10);
for (i = min(9, ilog2(UINT_MAX / new_clock)); i >= 0; i--) {
freq = clk_round_rate(ref_clk, new_clock << i);
- if (freq > (new_clock << i)) {
+ if (freq > new_upper_limit) {
/* Too fast; look for a slightly slower option */
freq = clk_round_rate(ref_clk, (new_clock << i) / 4 * 3);
if (freq > (new_clock << i))
@@ -181,6 +187,7 @@ static unsigned int renesas_sdhi_clk_update(struct tmio_mmc_host *host,
static void renesas_sdhi_set_clock(struct tmio_mmc_host *host,
unsigned int new_clock)
{
+ unsigned int clk_margin;
u32 clk = 0, clock;
sd_ctrl_write16(host, CTL_SD_CARD_CLK_CTL, ~CLK_CTL_SCLKEN &
@@ -194,7 +201,13 @@ static void renesas_sdhi_set_clock(struct tmio_mmc_host *host,
host->mmc->actual_clock = renesas_sdhi_clk_update(host, new_clock);
clock = host->mmc->actual_clock / 512;
- for (clk = 0x80000080; new_clock >= (clock << 1); clk >>= 1)
+ /*
+ * Add a margin of 1/1024 rate higher to the clock rate in order
+ * to avoid clk variable setting a value of 0 due to the margin
+ * provided for actual_clock in renesas_sdhi_clk_update().
+ */
+ clk_margin = new_clock >> 10;
+ for (clk = 0x80000080; new_clock + clk_margin >= (clock << 1); clk >>= 1)
clock <<= 1;
/* 1/1 clock is option */
--
2.25.1
next reply other threads:[~2022-09-22 8:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 8:55 Biju Das [this message]
2022-09-24 10:18 ` [PATCH v3] mmc: renesas_sdhi: Fix rounding errors Wolfram Sang
2022-09-25 17:06 ` Biju Das
2022-09-26 12:20 ` Geert Uytterhoeven
2022-09-26 12:52 ` Biju Das
2022-09-25 16:51 ` Wolfram Sang
2022-09-26 17:13 ` Biju Das
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220922085511.1078256-1-biju.das.jz@bp.renesas.com \
--to=biju.das.jz@bp.renesas.com \
--cc=Chris.Paterson2@renesas.com \
--cc=biju.das@bp.renesas.com \
--cc=geert+renesas@glider.be \
--cc=linux-mmc@vger.kernel.org \
--cc=linux-renesas-soc@vger.kernel.org \
--cc=prabhakar.mahadev-lad.rj@bp.renesas.com \
--cc=ulf.hansson@linaro.org \
--cc=wsa+renesas@sang-engineering.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).