linux-kernel - Re: [PATCH] mtd: revert "spi-nor: intel: provide a range for poll

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Message-ID: <e5f8203c-bf0a-3aee-a067-980592eab9e6@microchip.com>
Date:   Fri, 26 Jun 2020 10:57:26 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <luisalberto@...gle.com>
CC:     <miquel.raynal@...tlin.com>, <richard@....at>, <vigneshr@...com>,
        <mika.westerberg@...ux.intel.com>, <jethro@...tanix.com>,
        <bbrezillon@...nel.org>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mtd: revert "spi-nor: intel: provide a range for
 poll_timout"

On 6/11/20 1:46 AM, Luis Alberto Herrera wrote:
> This change reverts aba3a882a178: "mtd: spi-nor: intel: provide a range
> for poll_timout". That change introduces a performance regression when
> reading sequentially from flash. Logging calls to intel_spi_read without
> this change we get:
> 
> Start MTD read
> [   20.045527] intel_spi_read(from=1800000, len=400000)
> [   20.045527] intel_spi_read(from=1800000, len=400000)
> [  282.199274] intel_spi_read(from=1c00000, len=400000)
> [  282.199274] intel_spi_read(from=1c00000, len=400000)
> [  544.351528] intel_spi_read(from=2000000, len=400000)
> [  544.351528] intel_spi_read(from=2000000, len=400000)
> End MTD read
> 
> With this change:
> 
> Start MTD read
> [   21.942922] intel_spi_read(from=1c00000, len=400000)
> [   21.942922] intel_spi_read(from=1c00000, len=400000)
> [   23.784058] intel_spi_read(from=2000000, len=400000)
> [   23.784058] intel_spi_read(from=2000000, len=400000)
> [   25.625006] intel_spi_read(from=2400000, len=400000)
> [   25.625006] intel_spi_read(from=2400000, len=400000)
> End MTD read
> 
> Signed-off-by: Luis Alberto Herrera <luisalberto@...gle.com>
> ---
>  drivers/mtd/spi-nor/controllers/intel-spi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/controllers/intel-spi.c b/drivers/mtd/spi-nor/controllers/intel-spi.c
> index 61d2a0ad2131..2b89361a0d3a 100644
> --- a/drivers/mtd/spi-nor/controllers/intel-spi.c
> +++ b/drivers/mtd/spi-nor/controllers/intel-spi.c
> @@ -292,7 +292,7 @@ static int intel_spi_wait_hw_busy(struct intel_spi *ispi)
>         u32 val;
> 
>         return readl_poll_timeout(ispi->base + HSFSTS_CTL, val,
> -                                 !(val & HSFSTS_CTL_SCIP), 40,
> +                                 !(val & HSFSTS_CTL_SCIP), 0,

Would 10 us keep the performance as it was before?

Cheers,
ta