* [PATCH] i2c: altera: Use 64-bit arithmetic instead of 32-bit
@ 2020-02-10 19:26 Gustavo A. R. Silva
2020-02-10 20:42 ` Thor Thayer
2020-02-11 11:44 ` David Laight
0 siblings, 2 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-10 19:26 UTC (permalink / raw)
To: Thor Thayer; +Cc: linux-i2c, linux-kernel, Gustavo A. R. Silva
Add suffix ULL to constant 300 in order to avoid a potential integer
overflow and give the compiler complete information about the proper
arithmetic to use. Notice that this constant is being used in a context
that expects an expression of type u64, but it's currently evaluated
using 32-bit arithmetic.
Addresses-Coverity: 1458369 ("Unintentional integer overflow")
Fixes: 0560ad576268 ("i2c: altera: Add Altera I2C Controller driver")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
drivers/i2c/busses/i2c-altera.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
index 5255d3755411..526f453f0ff7 100644
--- a/drivers/i2c/busses/i2c-altera.c
+++ b/drivers/i2c/busses/i2c-altera.c
@@ -171,7 +171,8 @@ static void altr_i2c_init(struct altr_i2c_dev *idev)
/* SCL Low Time */
writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
/* SDA Hold Time, 300ns */
- writel(div_u64(300 * clk_mhz, 1000), idev->base + ALTR_I2C_SDA_HOLD);
+ writel(div_u64(300ULL * clk_mhz, 1000),
+ idev->base + ALTR_I2C_SDA_HOLD);
/* Mask all master interrupt bits */
altr_i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
--
2.25.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] i2c: altera: Use 64-bit arithmetic instead of 32-bit
2020-02-10 19:26 [PATCH] i2c: altera: Use 64-bit arithmetic instead of 32-bit Gustavo A. R. Silva
@ 2020-02-10 20:42 ` Thor Thayer
2020-02-11 11:44 ` David Laight
1 sibling, 0 replies; 3+ messages in thread
From: Thor Thayer @ 2020-02-10 20:42 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-i2c, linux-kernel
On 2/10/20 1:26 PM, Gustavo A. R. Silva wrote:
> Add suffix ULL to constant 300 in order to avoid a potential integer
> overflow and give the compiler complete information about the proper
> arithmetic to use. Notice that this constant is being used in a context
> that expects an expression of type u64, but it's currently evaluated
> using 32-bit arithmetic.
>
> Addresses-Coverity: 1458369 ("Unintentional integer overflow")
> Fixes: 0560ad576268 ("i2c: altera: Add Altera I2C Controller driver")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/i2c/busses/i2c-altera.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
> index 5255d3755411..526f453f0ff7 100644
> --- a/drivers/i2c/busses/i2c-altera.c
> +++ b/drivers/i2c/busses/i2c-altera.c
> @@ -171,7 +171,8 @@ static void altr_i2c_init(struct altr_i2c_dev *idev)
> /* SCL Low Time */
> writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
> /* SDA Hold Time, 300ns */
> - writel(div_u64(300 * clk_mhz, 1000), idev->base + ALTR_I2C_SDA_HOLD);
> + writel(div_u64(300ULL * clk_mhz, 1000),
> + idev->base + ALTR_I2C_SDA_HOLD);
>
> /* Mask all master interrupt bits */
> altr_i2c_int_enable(idev, ALTR_I2C_ALL_IRQ, false);
>
Thank you.
Reviewed-by: Thor Thayer <thor.thayer@linux.intel.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* RE: [PATCH] i2c: altera: Use 64-bit arithmetic instead of 32-bit
2020-02-10 19:26 [PATCH] i2c: altera: Use 64-bit arithmetic instead of 32-bit Gustavo A. R. Silva
2020-02-10 20:42 ` Thor Thayer
@ 2020-02-11 11:44 ` David Laight
1 sibling, 0 replies; 3+ messages in thread
From: David Laight @ 2020-02-11 11:44 UTC (permalink / raw)
To: 'Gustavo A. R. Silva', Thor Thayer; +Cc: linux-i2c, linux-kernel
From: Gustavo A. R. Silva
> Sent: 10 February 2020 19:27
>
> Add suffix ULL to constant 300 in order to avoid a potential integer
> overflow and give the compiler complete information about the proper
> arithmetic to use. Notice that this constant is being used in a context
> that expects an expression of type u64, but it's currently evaluated
> using 32-bit arithmetic.
>
> Addresses-Coverity: 1458369 ("Unintentional integer overflow")
> Fixes: 0560ad576268 ("i2c: altera: Add Altera I2C Controller driver")
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/i2c/busses/i2c-altera.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/busses/i2c-altera.c b/drivers/i2c/busses/i2c-altera.c
> index 5255d3755411..526f453f0ff7 100644
> --- a/drivers/i2c/busses/i2c-altera.c
> +++ b/drivers/i2c/busses/i2c-altera.c
> @@ -171,7 +171,8 @@ static void altr_i2c_init(struct altr_i2c_dev *idev)
> /* SCL Low Time */
> writel(t_low, idev->base + ALTR_I2C_SCL_LOW);
> /* SDA Hold Time, 300ns */
> - writel(div_u64(300 * clk_mhz, 1000), idev->base + ALTR_I2C_SDA_HOLD);
> + writel(div_u64(300ULL * clk_mhz, 1000),
> + idev->base + ALTR_I2C_SDA_HOLD);
Why not factor out the 100?
It may then be you can do 32bit arithmetic (3 * clk_mhz / 10).
If clk_mhz is MHz (not mHz) then the sum will never wrap 32 bits.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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