linux-kernel - Re: [PATCH 13/16] gpu: nova-core: Add support for VBIOS ucode extraction for boot

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Message-ID: <20250424191900.GA174004@joelnvbox>
Date: Thu, 24 Apr 2025 15:19:00 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Alexandre Courbot <acourbot@...dia.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Jonathan Corbet <corbet@....net>,
	John Hubbard <jhubbard@...dia.com>, Ben Skeggs <bskeggs@...dia.com>,
	Timur Tabi <ttabi@...dia.com>, Alistair Popple <apopple@...dia.com>,
	linux-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org,
	nouveau@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 13/16] gpu: nova-core: Add support for VBIOS ucode
 extraction for boot

On Wed, Apr 23, 2025 at 05:02:58PM +0200, Danilo Krummrich wrote:

[..]

> > >> +        data.extend_with(len, 0, GFP_KERNEL)?;
> > >> +        with_bar!(?bar0, |bar0_ref| {
> > >> +            let dst = &mut data[current_len..current_len + len];
> > >> +            for (idx, chunk) in dst
> > >> +                .chunks_exact_mut(core::mem::size_of::<u32>())
> > >> +                .enumerate()
> > >> +            {
> > >> +                let addr = start + (idx * core::mem::size_of::<u32>());
> > >> +                // Convert the u32 to a 4 byte array. We use the .to_ne_bytes()
> > >> +                // method out of convenience to convert the 32-bit integer as it
> > >> +                // is in memory into a byte array without any endianness
> > >> +                // conversion or byte-swapping.
> > >> +                chunk.copy_from_slice(&bar0_ref.try_read32(addr)?.to_ne_bytes());
> > >> +            }
> > >> +            Ok(())
> > >> +        })?;
> > >> +
> > >> +        Ok(())
> > >> +    }
> > ..actually initially was:
> > 
> > +        with_bar!(self.bar0, |bar0| {
> > +            // Get current length
> > +            let current_len = self.data.len();
> > +
> > +            // Read ROM data bytes push directly to vector
> > +            for i in 0..bytes as usize {
> > +                // Read byte from the VBIOS ROM and push it to the data vector
> > +                let rom_addr = ROM_OFFSET + current_len + i;
> > +                let byte = bar0.try_readb(rom_addr)?;
> > +                self.data.push(byte, GFP_KERNEL)?;
> > 
> > Where this bit could result in a lot of allocation.
> > 
> > There was an unsafe() way of not having to do this but we settled with
> > extends_with().
> > 
> > Thoughts?
> 
> If I understand you correctly, you just want to make sure that subsequent push()
> calls don't re-allocate? If so, you can just use reserve() [1] and keep the
> subsequent push() calls.
> 
> [1] https://rust.docs.kernel.org/kernel/alloc/kvec/struct.Vec.html#method.reserve



Ok that does turn out to be cleaner! I replaced it with the following and it works.

Let me know if it looks good now? Here's a preview:

-        data.extend_with(len, 0, GFP_KERNEL)?;
+        data.reserve(len, GFP_KERNEL)?;
+
         with_bar_res!(bar0, |bar0_ref| {
-            let dst = &mut data[current_len..current_len + len];
-            for (idx, chunk) in dst
-                .chunks_exact_mut(core::mem::size_of::<u32>())
-                .enumerate()
-            {
-                let addr = start + (idx * core::mem::size_of::<u32>());
-                // Convert the u32 to a 4 byte array. We use the .to_ne_bytes()
-                // method out of convenience to convert the 32-bit integer as it
-                // is in memory into a byte array without any endianness
-                // conversion or byte-swapping.
-                chunk.copy_from_slice(&bar0_ref.try_read32(addr)?.to_ne_bytes());
+            // Read ROM data bytes and push directly to vector
+            for i in 0..len {
+                // Read 32-bit word from the VBIOS ROM
+                let rom_addr = start + i * core::mem::size_of::<u32>();
+                let word = bar0_ref.try_read32(rom_addr)?;
+
+                // Convert the u32 to a 4 byte array and push each byte
+                word.to_ne_bytes().iter().try_for_each(|&b| data.push(b, GFP_KERNEL))?;
             }

Thanks.