linux-kernel - RE: [PATCH] spi: spi-fsl-lpspi: fix watermark truncation caused by type cast

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Message-ID:
 <VI2PR04MB11147DF123E2313B91CD8FBC7E8D5A@VI2PR04MB11147.eurprd04.prod.outlook.com>
Date: Fri, 21 Nov 2025 08:18:17 +0000
From: Carlos Song <carlos.song@....com>
To: Carlos Song <carlos.song@....com>, Frank Li <frank.li@....com>,
	"broonie@...nel.org" <broonie@...nel.org>, "rongqianfeng@...o.com"
	<rongqianfeng@...o.com>
CC: "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] spi: spi-fsl-lpspi: fix watermark truncation caused by
 type cast


Gently ping to avoid missing...

> -----Original Message-----
> From: carlos.song@....com <carlos.song@....com>
> Sent: Monday, November 17, 2025 11:04 AM
> To: Frank Li <frank.li@....com>; broonie@...nel.org; rongqianfeng@...o.com
> Cc: linux-spi@...r.kernel.org; imx@...ts.linux.dev; linux-kernel@...r.kernel.org
> Subject: [EXT] [PATCH] spi: spi-fsl-lpspi: fix watermark truncation caused by type
> cast
> 
> Caution: This is an external email. Please take care when clicking links or
> opening attachments. When in doubt, report the message using the 'Report this
> email' button
> 
> 
> From: Carlos Song <carlos.song@....com>
> 
> 't->len' is an unsigned integer, while 'watermark' and 'txfifosize' are u8. Using
> min_t with typeof(watermark) forces both values to be cast to u8, which
> truncates len when it exceeds 255. For example, len = 4096 becomes 0 after
> casting, resulting in an incorrect watermark value.
> 
> Use a wider type in min_t to avoid truncation and ensure the correct minimum
> value is applied.
> 
> Fixes: a750050349ea ("spi: spi-fsl-lpspi: use min_t() to improve code")
> Signed-off-by: Carlos Song <carlos.song@....com>
> ---
>  drivers/spi/spi-fsl-lpspi.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-fsl-lpspi.c b/drivers/spi/spi-fsl-lpspi.c index
> 8da66e101386..065456aba2ae 100644
> --- a/drivers/spi/spi-fsl-lpspi.c
> +++ b/drivers/spi/spi-fsl-lpspi.c
> @@ -486,7 +486,13 @@ static int fsl_lpspi_setup_transfer(struct spi_controller
> *controller,
>                 fsl_lpspi->tx = fsl_lpspi_buf_tx_u32;
>         }
> 
> -       fsl_lpspi->watermark = min_t(typeof(fsl_lpspi->watermark),
> +       /*
> +        * t->len is 'unsigned' and txfifosize and watermrk is 'u8', force
> +        * type cast is inevitable. When len > 255, len will be truncated in
> min_t(),
> +        * it caused wrong watermark set. 'unsigned int' is as the designated
> type
> +        * for min_t() to avoid truncation.
> +        */
> +       fsl_lpspi->watermark = min_t(unsigned int,
>                                      fsl_lpspi->txfifosize,
>                                      t->len);
> 
> --
> 2.34.1
>