linux-kernel - [PATCH AUTOSEL 4.9 09/19] dmaengine: qcom_hidma: comment platform_driver

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Message-Id: <20210524145106.2499571-9-sashal@kernel.org>
Date:   Mon, 24 May 2021 10:50:56 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Phillip Potter <phil@...lpotter.co.uk>,
        Vinod Koul <vkoul@...nel.org>, Sinan Kaya <okaya@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 09/19] dmaengine: qcom_hidma: comment platform_driver_register call

From: Phillip Potter <phil@...lpotter.co.uk>

[ Upstream commit 4df2a8b0ad634d98a67e540a4e18a60f943e7d9f ]

Place a comment in hidma_mgmt_init explaining why success must
currently be assumed, due to the cleanup issue that would need to
be considered were this module ever to be unloadable or were this
platform_driver_register call ever to fail.

Acked-By: Vinod Koul <vkoul@...nel.org>
Acked-By: Sinan Kaya <okaya@...nel.org>
Signed-off-by: Phillip Potter <phil@...lpotter.co.uk>
Link: https://lore.kernel.org/r/20210503115736.2104747-52-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/dma/qcom/hidma_mgmt.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/dma/qcom/hidma_mgmt.c b/drivers/dma/qcom/hidma_mgmt.c
index 82f36e466083..143ea7cad756 100644
--- a/drivers/dma/qcom/hidma_mgmt.c
+++ b/drivers/dma/qcom/hidma_mgmt.c
@@ -398,6 +398,20 @@ static int __init hidma_mgmt_init(void)
 		of_node_put(child);
 	}
 #endif
+	/*
+	 * We do not check for return value here, as it is assumed that
+	 * platform_driver_register must not fail. The reason for this is that
+	 * the (potential) hidma_mgmt_of_populate_channels calls above are not
+	 * cleaned up if it does fail, and to do this work is quite
+	 * complicated. In particular, various calls of of_address_to_resource,
+	 * of_irq_to_resource, platform_device_register_full, of_dma_configure,
+	 * and of_msi_configure which then call other functions and so on, must
+	 * be cleaned up - this is not a trivial exercise.
+	 *
+	 * Currently, this module is not intended to be unloaded, and there is
+	 * no module_exit function defined which does the needed cleanup. For
+	 * this reason, we have to assume success here.
+	 */
 	platform_driver_register(&hidma_mgmt_driver);
 
 	return 0;
-- 
2.30.2