linux-kernel - Re: Re: [PATCH 1/3] bits: introduce fixed-type genmasks

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Date: Wed, 24 Jan 2024 08:03:53 -0600
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Jani Nikula <jani.nikula@...ux.intel.com>
CC: Yury Norov <yury.norov@...il.com>, <linux-kernel@...r.kernel.org>,
	<dri-devel@...ts.freedesktop.org>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, <intel-xe@...ts.freedesktop.org>,
	<intel-gfx@...ts.freedesktop.org>
Subject: Re: Re: [PATCH 1/3] bits: introduce fixed-type genmasks

On Wed, Jan 24, 2024 at 09:58:26AM +0200, Jani Nikula wrote:
>On Tue, 23 Jan 2024, Lucas De Marchi <lucas.demarchi@...el.com> wrote:
>> From: Yury Norov <yury.norov@...il.com>
>>
>> Generalize __GENMASK() to support different types, and implement
>> fixed-types versions of GENMASK() based on it. The fixed-type version
>> allows more strict checks to the min/max values accepted, which is
>> useful for defining registers like implemented by i915 and xe drivers
>> with their REG_GENMASK*() macros.
>
>Mmh, the commit message says the fixed-type version allows more strict
>checks, but none are actually added. GENMASK_INPUT_CHECK() remains the
>same.
>
>Compared to the i915 and xe versions, this is more lax now. You could
>specify GENMASK_U32(63,32) without complaints.

Doing this on top of the this series:

-#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, 27)
+#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(62, 32)

and I do get a build failure:

./drivers/gpu/drm/i915/display/intel_cx0_phy.c: In function ‘__intel_cx0_read_once’:
./include/linux/bits.h:41:31: error: left shift count >= width of type [-Werror=shift-count-overflow]
    41 |          (((t)~0ULL - ((t)(1) << (l)) + 1) & \
       |                               ^~


I also tested them individually. All of these fail to build for me:

1)
-#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, 27)
+#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(32, 27)

2)
-#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, 27)
+#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, 31)

3)
-#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, 27)
+#define   XELPDP_PORT_M2P_COMMAND_TYPE_MASK            REG_GENMASK(30, -1)


Lucas De Marchi