linux-kernel - Re: [PATCH] spi: spi-mem: Add fix to avoid divide error

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Message-ID: <87msc5hc1a.fsf@bootlin.com>
Date: Thu, 24 Apr 2025 16:25:21 +0200
From: Miquel Raynal <miquel.raynal@...tlin.com>
To: Raju Rangoju <Raju.Rangoju@....com>
Cc: <broonie@...nel.org>,  <linux-spi@...r.kernel.org>,
  <linux-kernel@...r.kernel.org>,  Krishnamoorthi M
 <krishnamoorthi.m@....com>,  Akshata MukundShetty
 <akshata.mukundshetty@....com>
Subject: Re: [PATCH] spi: spi-mem: Add fix to avoid divide error


> --- a/drivers/spi/spi-mem.c
> +++ b/drivers/spi/spi-mem.c
> @@ -596,7 +596,11 @@ u64 spi_mem_calc_op_duration(struct spi_mem_op *op)
>  	ns_per_cycles = 1000000000 / op->max_freq;
>  	ncycles += ((op->cmd.nbytes * 8) / op->cmd.buswidth) / (op->cmd.dtr ? 2 : 1);
>  	ncycles += ((op->addr.nbytes * 8) / op->addr.buswidth) / (op->addr.dtr ? 2 : 1);
> -	ncycles += ((op->dummy.nbytes * 8) / op->dummy.buswidth) / (op->dummy.dtr ? 2 : 1);
> +
> +	/* Dummy bytes are optional for some SPI flash memory operations */
> +	if (op->dummy.nbytes)
> +		ncycles += ((op->dummy.nbytes * 8) / op->dummy.buswidth) / (op->dummy.dtr ? 2 : 1);
> +
>  	ncycles += ((op->data.nbytes * 8) / op->data.buswidth) / (op->data.dtr ? 2 : 1);
>  
>  	return ncycles * ns_per_cycles;

Reviewed-by: Miquel Raynal <miquel.raynal@...tlin.com>

Actually even address bytes sometimes may be skipped (eg. status reads). But there is no
reason for using spi_mem_calc_op_duration() in this case.

Thanks,
Miquèl