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Date: Tue, 31 Jan 2023 11:49:34 +0800
From: Tzung-Bi Shih <tzungbi@kernel.org>
To: Prashant Malani <pmalani@chromium.org>
Cc: linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev,
	bleung@chromium.org
Subject: Re: [PATCH] platform/chrome: cros_typec_vdm: Fix VDO copy
Message-ID: <Y9iPzvfJkxii390K@google.com>
References: <20230113182626.1149539-1-pmalani@chromium.org>
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In-Reply-To: <20230113182626.1149539-1-pmalani@chromium.org>

On Fri, Jan 13, 2023 at 06:26:26PM +0000, Prashant Malani wrote:
> The usage of memcpy() affects the representation of the VDOs as they are
> copied to the EC Host Command buffer. Specifically, all higher order
> bits get dropped (for example: a VDO of 0x406 just gets copied as 0x6).

memcpy() is byte-oriented; however, `vdo` is a pointer to u32.

> Avoid this by explicitly copying each VDO in the array. The number of
> VDOs generated by alternate mode drivers in their VDMs is almost always
> just 1 (apart from the header) so this doesn't affect performance in a
> meaningful way).

Although the patch has applied, I am wondering if the following would be a
better way to fix the issue:

memcpy(&vdm_req.vdm_data[1], vdo, (cnt - 1) * sizeof(*vdo));