Re: [PATCH] phy: freescale: phy-fsl-imx8-mipi-dphy: Fix hs_zero underflow

[Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>]

On Tue, Nov 10, 2026 at 02:05:46PM +0200, Stefan Ghetu wrote:
> From: "Oliver F. Brown" <oliver.brown@oss.nxp.com>
> 
> The hs_zero timing is computed as
> 
> 	n = (144 * (hs_clk_rate / 1000000) - 47500) / 10000;
> 	cfg->m_prg_hs_zero = n < 1 ? 1 : n;
> 
> hs_clk_rate is an unsigned long, so the subtraction is done unsigned and
> wraps for any rate below about 330 MHz, where 144 * MHz < 47500. Because
> n is a u32, the wrapped value is never seen as negative and the "n < 1"
> clamp does not take effect. The garbage value is then truncated into the
> 8-bit m_prg_hs_zero register field. At the minimum supported rate of
> 80 MHz this programs 199 on 64-bit and 181 on 32-bit, instead of the
> intended minimum of 1.
> 
> Make n signed and do the arithmetic in int so the clamp works on both
> 32-bit and 64-bit. The divided rate is at most 1500, so 144 * 1500 fits
> easily in an int.
> 
> Fixes: f4c8116e294b ("phy: Add driver for mixel mipi dphy found on NXP's i.MX8 SoCs")
> Cc: stable@vger.kernel.org
> Signed-off-by: Oliver F. Brown <oliver.brown@oss.nxp.com>
> Signed-off-by: Stefan Ghetu <stefan.ghetu@nxp.com>

Reviewed-by: Laurentiu Palcu <laurentiu.palcu@oss.nxp.com>

-- 
Thanks,
Laurentiu