dma_filter_fn(9)

💅 dma_filter_fn(9) — like, the callback filter for dma_request_channel, bestie

okay so this is dma_filter_fn(9) straight out of the Kernel API Manual, and honestly? it's giving tiny-but-mighty. one little callback, one huge job: deciding which DMA channel is the one. let's get into it 🎀

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✨ NAME ✨

dma_filter_fn — callback filter for dma_request_channel. that's it, that's the whole vibe. it's the bouncer at the channel club. 💅

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✨ SYNOPSIS ✨

bool dma_filter_fn (struct dma_chan *chan , void *filter_param );

like, yes, it returns a bool and yes, that's lowkey the whole point. ✨

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✨ ARGUMENTS ✨

• chan — the channel to be reviewed 🕵️‍♀️ like, this is the candidate, the one under the microscope, the main character of the moment.
• filter_param — an opaque parameter passed through dma_request_channel. opaque means don't look at it funny, it's not your business, it just rides along. 🙈

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✨ DESCRIPTION ✨

so here's the tea ☕: when this optional parameter is specified in a call to dma_request_channel, a suitable channel gets passed to this routine for further dispositioning before being returned. yes — further dispositioning. iconic word. she's doing admin work before the channel ever reaches you 🫶

and what even is "suitable"? glad you asked, bestie. 'suitable' indicates a non-busy channel that satisfies the given capability mask. so: not busy, and it matches the mask. both. no cap. 💯

it returns 'true' to indicate that the channel is suitable. that's the whole verdict — true means slay, come on in. 👑

ngl, the vibes are immaculate but the contract is strict: return 'true' only when the channel is genuinely suitable, and remember this whole thing is optional. you only get called if you show up. 🦋

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✨ SEE ALSO ✨

Kernel file ./include/linux/dmaengine.h, plus the whole extended friend group 💖:

• dma_cookie_t(9)
• enum dma_status(9)
• enum dma_transaction_type(9)
• enum dma_transfer_direction(9)
• struct data_chunk(9)
• struct dma_interleaved_template(9)
• struct dma_vec(9)
• enum dma_ctrl_flags(9)
• enum sum_check_bits(9)
• enum sum_check_flags(9)
• enum dma_desc_metadata_mode(9)
• struct dma_chan_percpu(9)
• struct dma_router(9)
• struct dma_chan(9)
• struct dma_chan_dev(9)
• enum dma_slave_buswidth(9)
• struct dma_slave_config(9)
• enum dma_residue_granularity(9)
• struct dma_slave_caps(9)
• struct dma_async_tx_descriptor(9)
• struct dma_tx_state(9)
• enum dmaengine_alignment(9)
• struct dma_slave_map(9)
• struct dma_filter(9)
• struct dma_device(9)
• dmaengine_prep_peripheral_dma_vec(9)
• dmaengine_prep_config_sg_safe(9)
• dmaengine_prep_config_single_safe(9)
• dmaengine_prep_dma_memset(9)
• dmaengine_terminate_all(9)
• dmaengine_terminate_async(9)
• dmaengine_synchronize(9)
• dmaengine_terminate_sync(9)
• dma_async_issue_pending(9)
• dma_async_is_tx_complete(9)
• dma_async_is_complete(9)

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okay that's the page!! 🌸 quick lil sign-off so you have the receipts: this one lives in ./include/linux, it's dated October 2026, and it's part of the Kernel API Manual. go forth and filter those channels, bestie — iykyk 💜✨🎀