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[193.154.207.67]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3ecd3555sm23765915f8f.42.2026.10.27.11.28.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Oct 2026 11:28:50 -0700 (PDT) Message-ID: <60d0962f-8769-49e8-9674-48ec98278529@gmail.com> Date: Tue, 27 Oct 2026 19:28:49 +0100 X-Mailing-List: dmaengine@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] dmaengine: pl08x: mark slave channels as DMA_PRIVATE To: Frank Li Cc: vkoul@kernel.org, Frank.Li@kernel.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261027070037.1809112-1-andi.platschek@gmail.com> Content-Language: en-US From: Andreas Gabriel-Platschek In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/27/26 3:39 PM, Frank Li wrote: > On Tue, Oct 27, 2026 at 08:00:37AM +0100, Andreas Gabriel-Platschek wrote: >> [You don't often get email from andi.platschek@gmail.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ] >> >> The pl08x slave engine channels are only ever handed out through >> explicit requests: DT clients go via pl08x_of_xlate() and the >> platform-data path uses dma_request_channel() with a filter, both of >> which end up in dma_get_slave_channel(). They are not meant to be >> published in the general-purpose channel table. >> >> Mark the slave device with DMA_PRIVATE at probe time so the dmaengine >> core treats it as always-private. Without this, if a dmaengine client >> is already active when the device is registered, >> dma_async_device_register() takes a reference on every channel, > Code change is okay. Are you sure the above description correct? where > code set it active when dma_async_device_register(). > > Frank I do think so, because async_damengine_get() -> dmaengine_get() is called from crypto/async_tx/async_tx.c and increments the dmaengine_ref_count. This way the dmaengine_ref_count is already >=1 before the pl08x dmaengine probes. dma_async_device_register() (in dmaengine.c) iterates over the channels inside of the following conditional:  if (dmaengine_ref_count && !dma_has_cap(DMA_PRIVATE, device->cap_mask)) and in there a dma_chan_get() is called for each channel and increments the client_count. With a client_count  >=1 we fail once pl08x_of_xlate()->dma_get_slave_channel() is called. setting DMA_PRIVATE prevents the client_count from being incremented by the core, keeping the client_count at 0 until a real client requests one hope that makes sense? best! Andi > >> and >> the subsequent dma_get_slave_channel() from pl08x_of_xlate() fails >> because the channel is no longer free (client_count != 0), leaving DT >> slave clients unable to acquire channels. >> >> The memcpy engine stays public as it is intended to be shared through >> the per-CPU channel table. >> >> Signed-off-by: Andreas Gabriel-Platschek >> --- >> drivers/dma/amba-pl08x.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c >> index 543c2eb8cfa8..06881d3f29a9 100644 >> --- a/drivers/dma/amba-pl08x.c >> +++ b/drivers/dma/amba-pl08x.c >> @@ -2775,6 +2775,7 @@ static int pl08x_probe(struct amba_device *adev, const struct amba_id *id) >> pl08x->has_slave = true; >> dma_cap_set(DMA_SLAVE, pl08x->slave.cap_mask); >> dma_cap_set(DMA_CYCLIC, pl08x->slave.cap_mask); >> + dma_cap_set(DMA_PRIVATE, pl08x->slave.cap_mask); >> pl08x->slave.dev = &adev->dev; >> pl08x->slave.device_free_chan_resources = >> pl08x_free_chan_resources; >> -- >> 2.47.3 >>