linux-kernel - Re: [PATCH 3/4] media: mediatek: vcodec: Fix mtk_vcodec_mem

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Message-ID: <6c693161-0e89-4f9d-9a92-18f3783eefd2@collabora.com>
Date:   Wed, 6 Dec 2023 11:19:32 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Fei Shao <fshao@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>, Tiffany Lin <tiffany.lin@...iatek.com>,
        Yunfei Dong <yunfei.dong@...iatek.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 3/4] media: mediatek: vcodec: Fix mtk_vcodec_mem_free()
 error log criteria

Il 13/11/23 13:26, Fei Shao ha scritto:
> mtk_vcodec_mem_free() shouldn't print error if the target DMA buffer has
> never been allocated or was freed properly in the previous call. That
> makes log confusing.
> 
> Update the error path to print log only when the caller attempts to free
> nonzero-size buffer with VA being NULL, which indicates something indeed
> went wrong.
> 
> This brings another benefit that the callers no more need to check
> mem->va explicitly to avoid the error, which can make the code more
> compact and neat.
> 
> Signed-off-by: Fei Shao <fshao@...omium.org>

I think that this error is supposed to catch two issues in one:
  - We're called to free no memory (something that does make no sense),
    this may happen for example when calling xxx_free() twice, and it
    is a mistake that *must* be fixed;
  - We're failing to free memory for real (which you covered)

....that said, I think that if you want to clarify the error messages
in this function, it should look something like this:

if (!mem->va) {
	mtk_v4l2_err(plat_dev, "%s: Tried to free a NULL VA", __func__);
	if (mem->size)
		mtk_v4l2_err(plat_dev, "Failed to free %lu bytes", mem->size);
	return;
}

Cheers,
Angelo