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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48fe537c788sm182556295e9.12.2026.05.17.07.02.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 17 May 2026 07:02:55 -0700 (PDT) Date: Sun, 17 May 2026 15:02:53 +0100 From: David Laight To: Peter Collingbourne Cc: Mark Brown , Patrice Chotard , Boris Brezillon , Christophe Kerello , linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] spi: use udelay() for short polling delays Message-ID: <20260517150253.031dec09@pumpkin> In-Reply-To: <20260517062554.117448-1-peter@pcc.me.uk> References: <20260517062554.117448-1-peter@pcc.me.uk> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-spi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 16 May 2026 23:25:54 -0700 Peter Collingbourne wrote: > A short polling delay, such as the delay of 5us > (SPINAND_READ_POLL_DELAY_US) provided by the SPI NAND driver, > can become a 1/HZ (order of ms) delay caused by the usleep_range() > call in read_poll_timeout(), significantly reducing SPI NAND access > performance. Fix it by implementing the polling delay with udelay() > (via read_poll_timeout_atomic()) if it is short enough, matching how > the initial delay is handled. > > Fixes: c955a0cc8a28 ("spi: spi-mem: add automatic poll status functions") > Signed-off-by: Peter Collingbourne > --- > drivers/spi/spi-mem.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c > index a09371a075d2..914e35e51cea 100644 > --- a/drivers/spi/spi-mem.c > +++ b/drivers/spi/spi-mem.c > @@ -1005,10 +1005,19 @@ int spi_mem_poll_status(struct spi_mem *mem, > usleep_range((initial_delay_us >> 2) + 1, > initial_delay_us); > > - ret = read_poll_timeout(spi_mem_read_status, read_status_ret, > - (read_status_ret || ((status) & mask) == match), > - polling_delay_us, timeout_ms * 1000, false, mem, > - op, &status); > + if (polling_delay_us < 10) > + ret = read_poll_timeout_atomic( > + spi_mem_read_status, read_status_ret, > + (read_status_ret || ((status)&mask) == match), > + polling_delay_us, timeout_ms * 1000, false, mem, > + op, &status); > + else > + ret = read_poll_timeout( > + spi_mem_read_status, read_status_ret, > + (read_status_ret || ((status)&mask) == match), > + polling_delay_us, timeout_ms * 1000, false, mem, > + op, &status); > + That looks rather sub-optional. Even if the interval is short you want to drop to sleeps if the device isn't responding. (Or this code is used for erases and you are doing a full device erase.) I doubt you want to spin for more than 1ms. -David > if (read_status_ret) > return read_status_ret; > }